A new series of quinazoline-4(3H)-one derivatives containing hydrazone, thiosemicarbazide, pyrazole moiety and 1,2,4triazolo[4,3-a]quinazolin-5-(4H)-one derivatives, were prepared in order to study the effect of such combinations on the expected antimicrobial activity.  Synthesis of target compounds (3-8) has been achieved through an interaction of the starting 2a or 2b with different alkyl or aryl isothiocyanate. Condensation of 2a or 2b with various aromatic aldehydes or ketones afforded the corresponding hydrazones 9-12. 1-(4-Pyridinyl)-1,2-dihydro-4phenyl(allyl)-1,2,4-triazolo[4,3-a]quinazolin-5-(4H)-one deriva tives 13, 14 have been synthesized through reflux of compound 9 or 10 in glacial acetic acid.  On the other hand, 1-(3-substituted-3,4dihydro-4-quinazolinon-2-yl)-3-(4-chlorophenyl) pyrazole-4-carbaldehyde 15 or 16 has also been synthesized through interaction of compounds 11 or 12 with Vilsmeier-Haack reagent1. The structures of the new compounds were assigned by spectral and elemental methods of analyses. The synthesized compounds were tested for their in vitro antibacterial and antifungal activities. The tested compounds showed moderate antibacterial activity and weak or no antifungal activity.