The amino acid sequence of the light chain of the vitamin K-dependent protein C from bovine plasma is reported together with the supporting data. The sequence was determined by sequenator analysis of intact light chain, which contains 155 amino acid residues, and fragments obtained by chemical and enzymatic degradation of the light chain. All 11 glutamyl residues up to position 44 are carboxylated as gamma-carboxyglutamic acid residues. This part of the molecule proved very homologous to the other vitamin K-dependent plasma proteins. The remaining part (111 residues) is homologous to the corresponding parts in factor IX and factor X but not to prothrombin.