Abstract: The VLE data for binary systems of N-methylpiperazine-piperazine and water-N- methylpiperazine were measured at pressure of 0.1013 MPa by using an improved Rose still.The experimental data of the systems were tested for thermodynamic consistency and correlated satisfactorily with Wilson equation.The critical properties,pc,Tc,V_c,and acentric factors,ω,of both N-methylpiperazine and piperazine have been estimated by group contribution method.The UNIFAC model was successfully used to correlate and predict VLE data of N-methylpiperazine-piperazine system．