In the course of our screening program for new antitumor antibiotics, two new piericidin family antibiotics, SN-198-D (1) and SN-198-B (2), were purified from the fermentation broth of Streptomyces sp. SN-198. The structures of SN-198-D (1) and SN-198-B (2) were elucidated as 7-demethylpiericidin A1 and 7-demethyl-3'-rhamnopiericidin A1, respectively, by UV, IR, FAB-MS, HRFAB-MS, and NMR analyses. Antimicrobial activities showed that SN-198-B (2) and 3'-rhamnopiericidin A1 (SN-198-C (4)) with sugar moiety had lower activity against some microorganisms than SN-198-D (1) and piericidin A1 (SN-198-E (3)) without sugar moiety. Cytotoxic activities revealed that SN-198-B (2) and SN-198-C (4) exhibited stronger cytotoxicity against epidermoid carcinoma KB and chronic myelogenous leukemia K562 cells than SN-198-D (1) and SN-198-E (3). The methyl moiety at C-7 had little effect on the biological activities of these compounds.