Protein Kinase C (PKC) is generally believed to play a central role in signal transduction, cellular growth control, gene expression, and tumor promotion. And it has been suggested that inhibitors of PKC might play important roles for the prevention and treatment of cancer. In order to investigate the possible inhibitors of PKC from natural products, PKC receptor binding assay was performed using bovine brain particulate as a source of PKC and the amount of $[^3H]Phorbol$ 12,13-dibutyrate (PDBu) bound to PKC was measured in the presence of test materials. Total methanol extracts from 100 kinds of natural products were partitioned into 3 fractions (n-hexane, ethyl acetate and aqueous layer) and their binding ability to the regulatory domain of PKC was evaluated. The ethyl acetate fractions of Morus alba $(roots,;IC_{50}:;156.6;{mu}g/ml)$, Rehmannia glutinosa $(roots,;IC_{50}:;134.3;{mu}g/ml)$, Lysimachia foenum-graecum $(roots,;IC_{50}:;167.8;{mu}g/ml)$, Polygonum cuspidata $(roots,;IC_{50}:;157.3;{mu}g/ml)$, Cnidium officinale $(aerial;parts,;IC_{50}:;145.2;{mu}g/ml)$, and the hexane $(IC_{50}:;179.3;{mu}g/ml)$ and the EtOAc fraction of Symplocarpus nipponicus $(roots,;IC_{50}:;155.9;{mu}g/ml)$ showed inhibitory activity of $[^3H]PDBu$ binding to PKC.