Abstract: Aim： To synthesize the ent-kaurene diterpenoid and its derivatives from natural available stevioside. Methods： The crucial pharmacophore of exo-methylene ketone was designed and the carboxyl group at C-4 was modifiedThe cytotoxic inhibition activities in vitro of target compounds were evaluated against human cancer cells BEL-7402，HO-8910，MCF-7 and HL-60 by a MTT method. Results and Conclusion： The structures of new target compounds were identified by ¹H NMR，FT-IR and EI-MS. The preliminary experimental results showed that some derivatives of ent-kaurene diterpenoid possessed fair inhibitory activity against tumor cell lines compared with that of their parent steviol.