A novel process for preparing oxazolidinone antibacterial agent Linezolid including key intermediates of oxazolidinones comprising: reacting 3-fluoro-4-morpholinyl aniline with R-epichlorohydrin; carbonylation to form oxazolidinone derivative; acetylation of (5R)-5-(chloromethyl)-3-(3-fluoro-4-morpholinophenyl-oxazolidin-2-one with sodium acetate to get novel intermediate; hydrolysis of (R)-3-(3-fluoro-4-morpholinophenyl)-2-oxo-5-oxazolidinyl methyl acetate; mesylation of (R)-3-(3-fluoro-4-morpholinophenyl)-2-oxo-5-oxazolidinyl methanol; reaction of (R)-3-(3-fluoro-4-morpholinophenyl)-2-oxo-5-oxazolidinyl methyl methane sulphonate with potassium phthalimide; hydrolysis of (S)-3-(3-fluoro-4-morpholinophenyl)-2-oxo-5-oxazolidinyl methyl phthalimide with hydrazine hydrate; acetylation of (S)-3-(3-fluoro-4-morpholinophenyl)-2-oxo-5-oxazolidinyl methyl amine with acetic anhydride yields Linezolid in high yield.