A series of 2,3-disubstituted 8-arylamino-3H-imidazo[4,5-g]quinazolines were synthesized and evaluated for their cytotoxic activity in vitro against five human cancer cell lines (human lung carcinoma cell line: A549, human leukemia cell lines: K562 and Molt-4, human prostate cancer cell line: PC-3, human breast carcinoma cell line: MDA-MB-231). Most of these compounds show potent activity against these tumor cell lines, especially against the A549 cell line. The cell cycle analysis was also studied by flow cytometry measurement on A549 cell line.