A series of 2-[N-aryl-2-oxo-2-(4-chlorophenyl)ethanehydrazonoyl]-6-methyl-4(3H)-pyrimidinones 5 were prepared by coupling the diazonium salt of aniline derivatives with 2-(4-chlorobenzoylmethylene)-6-methyl-4(3H)-pyrimidinone 4 in sodium hydroxide solution. The structures of these newly synthesized compounds were confirmed by IR, NMR, mass spectrometry and elemental analyses and the tautomeric structure of these compounds was discussed. All the newly synthesized compounds were screened for their antibacterial and antifungal activities, some of which exhibited moderate activity. Also, the above compounds were evaluated for their antitumor activity against a panel of 60 human tumor cell lines by the National Cancer Institute (NCI), USA. Compounds 5b, 5d and 5i showed good cytotoxic activities against the tested cell lines. In addition, the newly synthesized compounds were screened for their 5α-reductase inhibitor activity and all the tested compounds showed activities in descending order as follows 5b, 5c, 5g, 5j, 5d, 5h, 5f, 5e and 5i.