A phytochemical investigation on the aerial parts of Euphorbia helioscopia resulted in the isolation of 27 macrocyclic diterpenoids, including three previously unreported lathyrane derivatives, euphohelioscopoids A-C (1-3). Their structures were elucidated by spectroscopic data interpretation. Three jatrophanes, euphoscopin C (4), euphorbiapene D (6), and euphoheliosnoid A (5), showed cytotoxicity against a paclitaxel-resistant A549 human lung cancer cell line with IC50 values of 6.9, 7.2, and 9.5 μM, respectively, but were inactive against the parent A549 human lung cancer cell line (IC50 > 10 μM). It was found that jatrophanes with a benzoyloxy or a nicotinoyloxy substituent at C-7 showed more potent cytotoxic activity than their analogues containing acetyloxy and hydroxy groups at this position.