Ras proteins have been shown to be post-translationally farnesylated on a specific carboxy-terminal cysteine by protein farnesyltransferase (PFTase). Inhibition of PFTase is expected to alter membrane localization and activation of Ras proteins. In the course of screening for PFTase inhibitors of microbial origin, we have previously reported gliotoxins, pepticinnamins, and andrastins. Additional new PFTase inhibitors, kurasoins A and B (1 and 2), were found from the cultured broth of Paecilomyces sp. FO-3684. In this paper, taxonomy of the producing strain and fermentation, isolation, physico-chemical properties, and biological activities of kurasoins are described.