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 <i>R</i>, while the absolute configuration of ugonstilbene B was determined as 4a<i>S</i>,9a<i>R</i>. The synthesized compounds showed cytotoxic activities against selected human cancer cell lines.