A new group-contribution modified cell model equation of state (GCMCM EOS) has been developed to predict pressure-volume-temperature (PVT) properties of polymer melts. The equation uses monomer group contributions to estimate the characteristic parameters in the modified cell model (MCM EOS) proposed by Dee and Walsh [G.T. Dee, D.J. Walsh, Macromolecules 21 (1988) 811-817] for polymer molecules. Three molecular parameters per group were determined for 20 different groups. Average prediction error of specific volumes was 0.67% for 32 homopolymers and 1.01% for 20 copolymers and blend polymers over a wide range of temperature (277-671 K) and pressure (0.1-200 MPa). The average prediction error of PVT by GCMCM EOS was less than half of that by Parekh and Danner [V.S. Parekh, R.P. Danner, J. Polym. Sci., Part B 33 (1995) 395-402]. Furthermore, if one specific volume datum at atmospheric pressure is used, the average prediction error of PVT by GCMCM EOS could be reduced to 0.27% for the homopolymers and 0.34% for the copolymers and blend polymers.