The cyanogen bromide cleavage of "acetic" polyhedral protein from nuclear polyhedrosis virus of B. mori was performed. Two peptides BrCN-II and BrCN-II' which consist of 29 and 34 amino acid residue were isolated from a mixture of cyanogen bromide fragments. The amino acid composition and N-terminal amino acids were established. The tryptic proteolysis of these fragments was conducted and the tryptic peptides were separated. The amino acid composition of tryptic peptides was determined. The data obtained make it possible to consider these fragments to be internal areas of polypeptide chain of the protein under investigation.