Selenothioic acid S-alkyl esters were synthesized from the reaction of terminal acetylenes with n-butyllithium, selenium, and alkanethiols in moderate to high yields. The use of substituted benzenethiols or (triphenylsilyl)-acetylene. allowed for the isolation of S-aryl esters, The synthesis of alpha-aryl selenothioic acid S-alkyl esters was attained by the acid-catalyzed reaction of selenoacetic acid Se-alkynyl esters with thiols in good yields. Se-77 NMR studies showed that the chemical shifts in a series of the esters were downfield of that in selenoester by about 500 ppm and were upfield of that in selenoketone by about 600 ppm, In the visible spectra the absorptions of the esters were observed at about 340 and 568 nm. X-ray molecular structure analyses of alpha-silyl esters showed that the bond distances in the selenocarbonyl group were 1.792 and 1.785 Angstrom, respectively, The formation of 1,3-diselenetane was confirmed from the decomposed products of S-phenyl ester. The trend for the stability of selenothioic acid S-esters is discussed on the basis of these synthetic results.