Protein kinase C (PKC) was partially purified from Brassica campestris L., by successive chromatographies on DEAE-cellulose membrane, hydroxyapatite and phenyl-5PW columns. The purified preparation showed typical characteristics of the conventional type of mammalian PKC that responds to Ca2+, phosphatidylserine, and diacylglycerol or the tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate. The plant PKC activity was apparently associated with a 75-kDa polypeptide that was recognized by an antibody against the catalytic domain of rat PKC. Substrate specificity of the plant PKC was similar to that of the rat PKC. A synthetic peptide corresponding to residues 4-14 of myelin basic protein, which is a selective substrate for the mammalian PKC, was phosphorylated efficiently by the plant PKC. These results indicate the existence of a PKC equivalent in higher plant cells.