Supercritical fluid extraction was applied to obtain the lower polarity extracts from Croton crassifolius roots, and chemical investigation of which led to the isolation and identification of two new diterpenoids, named crassifolius P (1) and crassifolius Q (2). In vitro anti-proliferative activities of compounds 1 and 2 on A549, Hep-G2 and Hela tumor cell lines were evaluated. The two new compounds exhibited obvious selectivity to tumor cells with IC50 values ranging from 20.43 ± 1.18 μM to 25.72 ± 1.32 μM.
