A phytochemical investigation on Euphorbia alatavica Boiss resulted in the isolation of nine compounds, including two new ones, alatavolide and alatavoic acid (1-2). Chemical structures of these compounds were established on the basis of 1D, 2D NMR, and HR-MS techniques, and by comparison with data reported in the literature. Compounds 1, 2, 4, 6, 8, and 9 were screened for cytotoxicity using the MTT assay. Among these compounds, the new compound 2 showed moderate cytotoxicity against Hela, MCF-7 and A549 cell lines (IC50 values of 16.4 +/- 3.2, 14.5 +/- 2.8, 22.3 +/- 3.1 mu M, respectively), while the known compound 8 exhibited the most potent cytotoxicity with the IC50 values of 6.5 +/- 3.1, 1.9 +/- 0.9, 8.6 +/- 3.5 mu M, respectively.