Electrochemical oxidation and reduction processes of 2,5-dimercapto-1,3,4-thiadiazole (DMcT), 2-mercapto-5-methyl-1,3,4-thiadiazole, and bis(2-methyl-1,3,4-thiadiazolyl)-5,5’-disulfane (BMT) in non-aqueous acidic/basic media were examined. The oxidation potential of disulfide bond formation (0.9 V vs. Ag/AgCl/NaCl(sat of DMcT (SH-R-SH (R : 1,3,4-thiadiazole)) has been observed at 0.1 V in basic acetonitrile solution and was shifted to more positive potential (greater than 1.0 V) in acidic solution. Since SH-R-S- and S--R-S- possess higher HOMO levels (-4.2 eV and -0.7 eV respectively) than that of SH-R-SH (-9.2 eV), the proton-dissosiated thiol groups of adjoining DMcT molecules form disulfide bonds easily with oxidation. Furthermore, since the reduction potential of cleavage of the disulfide bond of BMT (-0.55 V) has been observed at -0.05 V in acidic acetonitrile, the electrochemically driven cleavage reaction of the disulfide bond has been accelerated in the presence of acid. From our experiments and calculations, it was clear that the proton plays an important role in both the oxidation and reduction processes of mercapto thiadiazoles.