Abstract: Five constituents were isolated from Dan-Shen (Salvia miltiorrhiza). Three of them were identified as miltirone (Ⅱ), ferruginol (Ⅰ) and Ro090680 (Ⅲ). The two others were named △¹-dehydromiltirone and △¹-dehydrotanshinone Ⅱ_A. Ro-090680 has been known as a potent inhibitor of rabbit platelet aggregation in vitro. Related tricyclic diterpenoids such as miltirone and ferruginol were also found to have the same activity.