3-Phenyl-6-methyl-4(3H)-quinazolinone-2-yl-mercaptoacetic acid hydrazide (3) was reacted with substituted aldehydes in absolute ethanol to obtain a new series, 3-phenyl-6-methyl-4(3H)-quinazolinone-2-yl-mercaptoacetic acid arylidenehydrazides (4a-q). The structures of 4a-q were elucidated by elemental analyses and from spectrometric (UV, IR, H-1-NMR, C-13-NMR and EIMS) data. Then 4a-q were evaluated for antibacterial, antifungal and antitubercular activities. No significant activity was observed against the selected microorganisms.