Phytochemical studies on Senna skinneri and Senna wislizeni have resulted in the isolation of rutin (1), quercetin (2), the new flavonol 5,7-dimethoxyrutin (la) and the aglycon 5,7-dimethoxyquercetin (2a), which is reported for the first time from a natural source. These compounds showed mutagenic activity in Salmonella thyphimurium. D-3-O-methyl-chiro-inositol (3) is reported for the first time in the genus Senna. the stilbenoid piceatannol (4) was isolated from roots of Senna skinneri, and showed antimicrobial activity against S. typhimurium and E. coli.