A cytotoxic principle was newly isolated from Chrysosplenium grayanum MAXIM. (Saxifragaceae) and identified as beta-peltoboykinolic acid (1) on the basis of spectral data. Cytotoxicity of compound 1 was tested against various human cancer cell lines in vitro, and antitumor effect of this compound was demonstrated on Meth . A mouse fibrosarcoma. The experiment of combined treatment with compound 1, mitomycin C, and OK-432 resulted in enhancing the antitumor effect against B16-BL6 mouse melanoma in C57BL/6 mice.