Abstract: AimTo study the synthesis and antitumour activities of some aryl-substituted pteridines. MethodsA series of aryl-substituted pteridines were synthesized from 4,6-diamino-5-nitrosopyrimidines by cyclization with 4-aminophenylacetonitriles. The antitumour activities were tested by MTT method. Results Nine new compounds (I-III) were synthesized and their structures were characterized by EA, IR,¹HNMR and MS spectra. Compounds I-III showed antitumour activities in vitro. ConclusionCompounds I-III showed remarkable antitumour activities in vitro. No interaction was determined between the title compounds and calf thymus DNA. It indicated that these compounds possibly inhibit dihydrofolate reductase (DHFR) or other enzymes on which folic acid depends.