Seventeen compounds (2-18) synthetized from the diterpenoid ent-beyer-15-en-18-ol (1) isolated from aerial part of Baccharis tola were tested for their gastroprotective activity on the model of HCl/EtOH-induced gastric lesions in mice. Furthermore cytotoxicity test toward fibroblasts and AGS cells were performed. The results showed that compound 1 (ED<inf>50</inf> = 50 mg/kg), 2, 6 and 13 were the most active regarding gastroprotective activity. Compounds 8-10 and 17-18 showed the lowest cytotoxicity toward fibroblasts and AGS cells. Regarding to mode of gastroprotective action, the effect elicited by 6 (50 mg/kg) was reversed by Indomethacin but not by N-ethylmaleimide, N^G-nitro-l-arginine methyl ester or ruthenium red, which suggests that prostaglandins are involved in the mode of gastroprotective action of 6.