The biotransformation of cinobufagin by cell suspension cultures of Catharanthus roseus was investigated. After 6 days incubation, four new glucosylated derivatives, desacetylcinobufagin 16-O-β-D-glucoside, 3-epi-desacetylcinobufagin 16-O-β-D-glucoside, 3-oxo-desacetylcinobufagin 16-O-β-D-glucoside, and cinobufagin 3-O-β-D-glucoside, respectively, were isolated and identified on the basis of their physical and chemical data. This is the first report of bufadienolides with a glucosyl substituent at the C-16 position.