In this study, 3-substituted-5-(4-carboxycyclohexyl-methyl)-tetrahydro-2H-1,3,5-thiadiazine-2-thione which have phenylethyl (1), octyl (2), cyclopropyl (3), 4-methoxybenzyl (4), phenyl (5) groups in position 3 have been synthesized and examined for antimicrobial activities. Their structures were elucidated by spectral method. Antibacterial activities of these compounds against Gram-positive bacteria (Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212), gram-negative bacteria (Escherichia coli ATCC 2592, Pseudomonas aeruginosa ATCC 27853) and yeast-like fungi (Candida albicans ATCC 10231, Candida parapsilosis ATCC 90018) were investigated by the micro-dilution method and compared with the activity of sulbentine, ciprofloxacin and flucanozole. By this way their minimal inhibitory concentration (MIC) values were determinated. Compounds 1-4 exhibited almost equally potent activity against Staphylococcus aureus ATCC 29213 (MIC: 31.2 mu g/mL). Compounds 1,3,4 showed similar antibacterial activity against Enterococcus faecalis ATCC 29212) (MIC: 62.5 mu g/mL). None of the compounds exhibited activity against Gram-negative bacteria. On the other hand, all compounds had potent antifungal activities against the yeast utilized. Compounds 1-4 displayed significant antifungal activity against Candida parapsilosis ATCC 90018 at 7.8 mu g/mL concentration while sulbentine was active at 125 mu g/mL. Among the synthesized compounds, 3- cyclopropyl-5-(4-carboxycyclohexyl-methyl)tetrahydro-2H-1,3,5-thiadiazine-2-thione(3) seems to be the most effective compound with antibacterial and antifungal activity.