Catharanthus roseus cell suspension cultures were employed for the biotransformation of 2alpha,5alpha,10beta,14beta-tetraacetoxy-4(20),11-taxadiene ( 1), and four metabolites were obtained. Based on their physical and chemical data, the structures of the four metabolites were respectively elucidated as 10beta-hydroxy-2alpha,5alpha,14beta-triacetoxy-4(20),11-taxadiene (2), 5alpha-hydroxy-2alpha,10beta, 14beta-triacetoxy-4(20),11-taxadiene (3), 6alpha,10beta-dihydroxy-2alpha,5alpha,14beta-triacetoxy-4(20),11-taxadiene (4), and 6alpha,9alpha,10beta-trihydroxy-2alpha,5alpha,14beta-triacetoxy-4(20),11-taxadiene (5), among which 3 and 5 were characterized as new taxoids. The effects of the stages of substrate addition on the biotransformation were also investigated. The results revealed that the biotransformation rate for 1 reached 85.3 % and the yield of 2 70 % when 1 was administered during the mid-linear phase (9 - 12 th day) of the cell growth cycle. On the other hand, the yield for 4 reached the highest level of 11.8 % when 1 was added in the early linear phase (6 th day).