We report the synthesis of 5-hydroxy-7-methoxy-2-phenyl-4-quinolones and their biological activity as antitumor agents. These molecules were initially evaluated for their ability to induce cell cycle arrest in the G2/M phase. Compounds that showed significant G2/M cell cycle arrest were tested for antiproliferative activity using both the MTT assay and the NCI in vitro 60 cell line human tumor screen. The 5-hydroxy-7-methoxy-2-phenyl-4-quinolone (3a) and 2-(3-fluorophenyl)-5-hydroxy-7-methoxy-4-quinolone (3f) were the most active in the cell cycle arrest test whereas 3f was found to be the most active in the MTT assay. In terms of structural requirements, we found that the presence of a 5-hydroxyl group, a 7-methoxy group, and an unsubstituted N1 were essential for the antimitotic activity. In accordance with the literature, a fluoro group at the 3'- or 2'-position and a methoxy or a chloro group at the 3'-position were found to be highly advantageous for both the cell cycle arrest and the antiproliferative activities.