Ten new 4-thiazolidinone derivatives have been synthesized from the alkanoic acids. Alkanoic acid hydrazides (I) on refluxing with aromatic aldehydes in the presence of a catalytic amount of glacial acetic acid in methanol furnish corresponding hydrazones (II). Thioglycolic acid react with (II) in methanol yield the title compounds (III). These 4-thiazolidinone derivatives were characterized by CHN analysis, IR and 1H NMR spectral data. All the compounds were evaluated for their in vitro antimicrobial activity against two Gram negative strains (Escherichia coli and Pseudomonas aeruginosa) and two Gram positive strains (Bacillus subtilis and Staphylococcus aureus) and fungal strain Candida albicans and Aspergillus niger. All newly synthesized compounds exhibited promising results.