The synthesis and pharmacological evaluation of new [(2-oxobenzothiazolin-3-yl)-methyl]-4-alkyl/aryl-1,2,4-triazoline-5-thiones are reported. All compounds were screened for analgesic and antiinflammatory activities by using the AcOH induced-stretching test, the hot plate test, the tail clip test, and the tail flick test. All of the title compounds showed more potent activity than the standard compound aspirin in the AcOH induced-stretching test. In the hot plate test [(2-oxobenzothiazolin-3-yl)methyl]-4-phenethyl-1,2,4-triazoline-5-thione 5j were revealed to be two-fold more potent in antinociceptive activity than novalgine. However, in the tail flick and tail clip test none of the compounds showed an antinociceptive activity as high as that of novalgine. On the basis of available data the structure-activity relationship in the [(2-oxobenzothiazolin-3-yl)methyl]-4-alkyl/aryl-1,2,4-triazoline-5-thiones was also discussed.