This study describes the first and efficient syntheses of the naturally occurring ugonstilbenes A, B, and C. The stilbene skeleton was prepared using the Horner-Wadsworth-Emmons reaction. On the basis of their specific rotations, the absolute configurations of ugonstilbenes A and C were both determined to be R, while the absolute configuration of ugonstilbene B was determined as 4aS,9aR. The synthesized compounds showed cytotoxic activities against selected human cancer cell lines.