A series of novel oxadiazinan-5-one namely 2-methyl-2-phenyl-1,3,4-oxadiazinan-5-one (6), 2-(3-hydroxyphenyl)-2-methyl-1,3,4-oxadiazinan-5-one (7), 2-(4-hydroxyphenyl)-2-methyl-1,3,4-oxadiazinan-5-one (8), 2-(2, 4-dihydroxyphenyl)-2-methyl-1,3,4-oxadiazinan-5-one (9) and 2-(2,5-dihydroxyphenyl)-2-methyl-1,3,4-oxadiazinan-5-one (10) have been synthesized by the reaction of acetophenone and its derivatives with cyanoacetic acid hydrazide. The structural assignments of the products were done on the basis of IR, 1 H NMR, 13C NMR, MS, and analytical data. The in vitro antioxidant and antimicrobial activity of all the synthesized compounds (6–10) was tested by the DPPH and disk diffusion method, respectively. The synthesized compounds were screened against Gram-positive and Gram-negative bacterial and fungal strains. Compound (7) showed the highest inhibition comparable with the standard antibiotic drugs Ciprofloxacin and Amphotericin B. The antibacterial activity of the synthesized compounds was further investigated with the help of in silico docking study using Discovery studio 3.1, Molego Virtual Docker and LigandScout to predict the active sites.