The pitting corrosion behaviour of type UNS S31603 stainless steel ( 316L SS) in 0.01, 0.05 and 0.1 M thiosulfate ion (S2O32-) in the absence and presence of various concentrations of chloride ion ( Cl-) was studied using the cyclic potentiodynamic polarization method. The influence of major factors which affect pitting corrosion such as pH and temperature, were also investigated. It was found that both the pitting potential ( E-pit) and the repassivation potential ( E-rp) decreased with increase in Cl- concentration and solution temperature and a more pronounced difference in E-pit values for various concentrations of S2O32- in 1.0 M Cl- was obtained at lower temperatures. The effect of pH on E-pit, E-corr and E-rp values for different concentrations of S2O32- in the presence of 1.0 M Cl- was also determined.