The interfacial activity of 8-mercaptoquinoline (QSH) and its complexation kinetics with Ni(II) in the toluene-water phase pair have been studied and compared to the oxygen analogs, 8-quinolinol and its derivatives. Unlike the 8-quinolinols, QSH exhibited substantial interfacial activity in its neutral form. The interfacial activity of QSH may stem from its zwitterion form QH+S-. The interfacial excess of QS- is 1-2 orders of magnitude larger, and its distribution constant between the aqueous phase and interface is an order to magnitude larger, than those of 8-quinolinates. The rate limiting step in the complexation of Ni(II) by QSH and QS- is the formation of the 1:1 complex, NiQS+ as in the case of 8-quinolinols. The bulk rate constants for QSH and QS- are similar to the 8-quinolinols. As expected from the interfacial activity of QSH, it exhibited interfacial reactivity toward Ni(H), but with a smaller rate constant compared to the bulk value. The interfacial rate constant for QS- was only twice that of its value in the bulk aqueous phase, in marked contrast to the 8-quinolinates which exhibited increases by factors of 10-25.