3-[(4-Substituted) (2-oxo-1,3-oxazolidin-3-yl)-phosphoryl]-1,3-oxazolidin-2-ones (4a–j) were synthesized through a two-step process. Bis-(2-oxo-1,3-oxazolidin-3-yl)-phosphonic chloride (2) prepared by the reaction of two moles of oxazolidin-2-one (1) with phosphorus oxychloride in dry tetrahydrofuran in the presence of triethylamine and treatment with various heterocyclic aromatic and aliphatic amines under the same experimental conditions afforded the title compounds (4a–j). They were characterized by elemental analysis, IR,NMR(1H, 13Cand 31P) and mass spectroscopy. Their antimicrobial activities were also evaluated.Keywords: 3-[(4-Substituted) (2-oxo-1,3-oxazolidin-3-yl)-phosphoryl]-1,3-oxazolidin-2-ones, oxazolidin-2-one, bis-(2-oxo-1,3-oxazolidin-3-yl)-phosphonic chloride, antimicrobial activity, spectral studie