A two parameters equation of state (EOS) for nonaqueous electrolyte solutions system has been developed. The equation is in terms of Helmholtz free energy and incorporated with results of low density expansion of non-primitive mean spherical approximation. The EOS was tested for experimental data reported in literatures of 9 nonaqueous single electrolyte solutions of which the temperature was 298.15K, and it also has a good predictive capability for nonaqueous electrolyte solutions at different temperature in this work. The comparasions with EOSs published earlier by other researchers in literatures are carried out in detail.