New 4-thiazolidinone derivatives of benzilic acid (${alpha},{alpha}$-diphenyl-${alpha}$-hydroxyacetic acid) have been synthesized and evaluated for antibacterial and antifungal activities. The reaction of 1-(${alpha},{alpha}$-diphenyl-${alpha}$-hydroxy)acetyl-4-alkyl/arylthiosemicarbazides with ethyl 2-bromopropionate gave 3-alkyl/aryl-2-[((${alpha},{alpha}$-diphenyl-${alpha}$-hydroxy)acetyl)hydrazono]-5-methyl-4-thiazolidinone derivatives. Their antibacterial and antifungal activities were evaluated against S. aureus ATCC 29213, P. aeruginosa ATCC 27853, E. coli ATCC 25922, C. albicans ATCC 10231, C. parapsilosis ATCC 22019, C. krusei ATCC 6258, T. mentagrophytes var. erinacei NCPF 375, M. gypseum NCPF 580 and T. tonsurans NCPF 245. 3e, 3f, 3g and 3h showed the highest antibacterial activity. Particularly 3a and 3e showed the highest antifungal activities against C. parapsilosis ATCC 22019, T. tonsurans NCPF 245 and M. gypseum NCPF 580.