Abstarct: The purpose of this work is to extend the linear isotherm reqularity equation of state (LIR-EOS) to esters using group contribution method. According to the concept of group contribution method, esters considered as a mixture of their constituent groups. Then LIR equation of state is being extended to this mixture. Furthermore the temperature dependency of equation of state parameters were determined. In the next step, the contribution of constituent groups were determined for the parameters of this EOS. To do so three basic compounds, namely propan, n-butane and cyclohexane, were used to obtain the contribution of methyl and methylene groups in the EOS parameters. Also the ethyl propionate was used to obtain the contribution of ester functional group. Hence, having the group contributions in the equation of state parameters and the mean geometric approximation, according to the dependency of equation of state parameters to the composition of system, we may calculate the EOS parameters for other esters in each temperatures. Then using the calculated values of equation of state parameters, we may predict the density of each sters at different pressures and temperatures. Average persentage error in density prediction of esters were found to be lower than 3%.