The scaled hypersphere search method was applied to ab initio potential energy surfaces of the H2S center dot(H2O)(n)/SH-center dot H3O+center dot(H2O)(n-1) system with n = 5-7. Local minima databases including 121, 326, and 553 structures for n = 5-7, respectively, were obtained based on calculations at the MP2/6-311++G(3df,2p)//B3LYP/631+G** level. In these small cluster sizes, the SH-center dot H3O+center dot H2O)(n-1) type is still unstable relative to the H2S center dot(H2O)(n) type, and the global minima for H2S center dot(H2O)(n-1) are very similar to those of pure water clusters of (H2O)(n+1). Thermodynamic simulations based on the present databases showed a structure transition from the wellmixed (H2O)(n+1)-like global minimum at low temperatures to unmixed complexes between H2S and (H2O)(n) at high temperatures.