A series of some new 3-benzyl-2-phenyl-4(5H)-(substituted phenylhydrazino)-1, 3-oxazolidines 6a-f derivatives were synthesized. The in vitro anti-bacterial and anti-fungal activities were determined by paper disk diffusion method. The minimum inhibitory concentrations (MIC) of the compounds were also determined by agar streak dilution method. Most of the synthesized compounds exhibited significant anti-bacterial and anti-fungal activities. Among the synthesized compounds 3-benzyl-2-phenyl-4(5H)-4'methoxyphenyl hydrazino-1, 3-oxazolidine (6d) and 3- benzyl-2-phenyl-4(5H)-4'acetamidophenyl hydrazino-1, 3-oxazolidine (6e) exhibited most potent in vitro antimicrobial activity against Staphylococcus aureus, Staphylococcus epidermidis, Micrococcus luteus, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Aspergillus niger and Candida albicans.