Two new megastigmane, cucumegastigmanes I (1) and II (2), together with a known megastigmane, (+)-dehydrovomifoliol (3), and five other known compounds were isolated from the leaves of Cucumis sativus. The structures of the new compounds were elucidated from spectroscopic analysis and their absolute stereochemistries were determined in detail using the chemical conversion and a modified Mosher's method.