A series of cyclopentadienylnickelthiolate complexes, [Ni(PBu3)(eta(5)-C5H5)(SC6H4X-4)] (X=F, Cl, Br, NH2), were shown to express stable reversible electrochemical properties even after formation of SO2 adducts in organic phase consisting of argon purged CH2Cl2/0.1 M [n-Bu4N][BF4]. The formal potentials (E-ot) values of the compounds ranged from 265 to 431 mV/Ag-AgCl depending on the para substituent of the benzene thiolate ligand. Electrochemical, UV-vis and H-1 NMR spectroscopic analyses show that the formation of SO2 adducts causes the perturbation of the electronic density of the nickel metal center, indicated by shifts in the E-ot values of the Ni-II/III redox couple that is dependent on SO2 concentration. The detection limits of the resulting organic phase electrochemical gas sensor system was as low as 0.56 ppm SO2 for the fluoro complex, while the linear range was as high as 700 - 2000 ppm SO2 for the amino complex.