diff --git a/src/fmt/fmt_internal.h b/src/fmt/fmt_internal.h
index f472c47c..48481aad 100644
--- a/src/fmt/fmt_internal.h
+++ b/src/fmt/fmt_internal.h
@@ -6,6 +6,7 @@
 #ifndef NURI_FMT_FMT_INTERNAL_H_
 #define NURI_FMT_FMT_INTERNAL_H_
 
+#include <cstddef>
 #include <functional>
 #include <iterator>
 #include <string>
@@ -97,15 +98,14 @@ void pdb_update_confs(Molecule &mol, const std::vector<AT> &atom_data,
 constexpr int kChainIdx = 0;
 
 template <class RT, class AT, class ChainAsSv, class ResidueMember,
-          class SeqMember, class ICodeAsSv,
+          class SeqMember, class ICodeAsSv, class EntityMember = std::nullptr_t,
           std::enable_if_t<!std::is_reference_v<RT>, int> = 0>
-// NOLINTNEXTLINE(*-missing-std-forward)
-void pdb_update_substructs(Molecule &mol, RT &&residues,
-                           const std::vector<AT> &atoms,
-                           const ChainAsSv &chain_sv,
-                           const ResidueMember &residue_member,
-                           const SeqMember &seq_member,
-                           const ICodeAsSv &icode_sv) {
+void pdb_update_substructs(
+    // NOLINTNEXTLINE(*-missing-std-forward)
+    Molecule &mol, RT &&residues, const std::vector<AT> &atoms,
+    const ChainAsSv &chain_sv, const ResidueMember &residue_member,
+    const SeqMember &seq_member, const ICodeAsSv &icode_sv,
+    const EntityMember &eid_member = nullptr) {
   auto &subs = mol.substructures();
 
   std::vector<std::pair<std::string_view, std::vector<int>>> chains;
@@ -138,6 +138,11 @@ void pdb_update_substructs(Molecule &mol, RT &&residues,
     if (!icode.empty())
       sit->add_prop("icode", icode);
 
+    if constexpr (!std::is_same_v<EntityMember, std::nullptr_t>) {
+      sit->add_prop("entity_id",
+                    std::invoke(eid_member, atoms[sit->atom_ids()[0]]));
+    }
+
     ABSL_DCHECK(sit->props()[kChainIdx].first == "chain");
   }
 
@@ -146,6 +151,11 @@ void pdb_update_substructs(Molecule &mol, RT &&residues,
     sit->update(std::move(chain.second), {});
     sit->name() = chain.first;
     sit->set_id(i);
+
+    if constexpr (!std::is_same_v<EntityMember, std::nullptr_t>) {
+      sit->add_prop("entity_id",
+                    std::invoke(eid_member, atoms[sit->atom_ids()[0]]));
+    }
   }
 }
 }  // namespace internal
diff --git a/src/fmt/mmcif.cpp b/src/fmt/mmcif.cpp
index 634fcbfa..4f69ed65 100644
--- a/src/fmt/mmcif.cpp
+++ b/src/fmt/mmcif.cpp
@@ -367,7 +367,8 @@ std::string as_key(std::string_view prefix, std::string_view alt_id) {
 
 class MmcifAtomData {
 public:
-  explicit MmcifAtomData(MmcifAtomInfo first): data_ { first } { }
+  explicit MmcifAtomData(MmcifAtomInfo first, std::string_view entity_id)
+      : data_ { first }, entity_id_(entity_id) { }
 
   bool add_info(MmcifAtomInfo info) {
     ABSL_DCHECK(static_cast<bool>(info));
@@ -422,8 +423,11 @@ class MmcifAtomData {
     return static_cast<int>(it - data_.begin());
   }
 
+  std::string_view entity_id() const { return entity_id_; }
+
 private:
   std::vector<MmcifAtomInfo> data_;
+  std::string_view entity_id_;
 };
 
 struct MmcifResidueInfo {
@@ -611,7 +615,7 @@ class MmcifModelData {
   explicit MmcifModelData(int model_num): model_num_(model_num) { }
 
   void add_atom(MmcifAtomInfo info, std::string_view comp_id,
-                const internal::CifValue &id) {
+                std::string_view entity_id, const internal::CifValue &id) {
     ABSL_DCHECK(static_cast<bool>(info));
 
     int ri = residues_.prepare_add_atom(info, comp_id, id);
@@ -622,6 +626,14 @@ class MmcifModelData {
     const int ai = it->second;
 
     if (!first) {
+      if (entity_id != atoms_[ai].entity_id()) {
+        ABSL_LOG(WARNING)
+            << "Entity ID mismatch: " << entity_id << " vs "
+            << atoms_[ai].entity_id() << "; "
+            << "ignoring atom with serial number " << info.id().atom_id;
+        return;
+      }
+
       bool new_altloc = atoms_[ai].add_info(info);
       ABSL_LOG_IF(WARNING, !new_altloc)
           << "Duplicate atom " << info.id().atom_id << " of residue "
@@ -630,7 +642,7 @@ class MmcifModelData {
       return;
     }
 
-    atoms_.push_back(MmcifAtomData(info));
+    atoms_.push_back(MmcifAtomData(info, entity_id));
     residues_.add_atom_at(ri, ai);
   }
 
@@ -660,7 +672,8 @@ class MmcifModelData {
     internal::pdb_update_substructs(mol, std::move(residues_), atoms_,
                                     &ResidueId::asym_id,
                                     &MmcifResidueInfo::comp_id,
-                                    &ResidueId::seq_id, &ResidueId::ins_code);
+                                    &ResidueId::seq_id, &ResidueId::ins_code,
+                                    &MmcifAtomData::entity_id);
     return mol;
   }
 
@@ -701,7 +714,9 @@ std::vector<Molecule> mmcif_read_next_block(CifParser &parser) {
                     alt_id = NullableCifColumn::from_key(
                         block.data(), "_atom_site.label_alt_id"),
                     type_symbol = NullableCifColumn::from_key(
-                        block.data(), "_atom_site.type_symbol");
+                        block.data(), "_atom_site.type_symbol"),
+                    entity_id = NullableCifColumn::from_key(
+                        block.data(), "_atom_site.label_entity_id");
 
   TypedNullableColumn<absl::SimpleAtof, false> occupancy =
       NullableCifColumn::from_key(block.data(), "_atom_site.occupancy");
@@ -741,7 +756,7 @@ std::vector<Molecule> mmcif_read_next_block(CifParser &parser) {
     if (first)
       models.push_back(MmcifModelData(mid));
 
-    models[it->second].add_atom(info, *comp_id[i], id);
+    models[it->second].add_atom(info, *comp_id[i], *entity_id[i], id);
   }
 
   StructConnIndexer ptnr1(block.data(), res_idx, 0),