A theoretical equation of state (EOS) for chain molecule fluids is presented based on an improved hole and cell model in which the geometries of both the cells and the mers are defined as the dodecahedrons and reasonably related with the Lennard-Jones potential. Furthermore the number of configurations is treated to contribute to the EOS by means of minimizing the Helmholtz free energy to determine the cell size. This study may be regarded as the improved theories about the hole and cell model proposed by Simha et al. and the hole model by Sanchez and Lacombe. The present EOS has three characteristic parameters per pure fluid, which can lead to a corresponding-state principle for pure polymeric fluids. The validity and applicability of the equation were investigated by correlating the experimental PVT data for some common polymers and predicting the thermal expansion coefficient and isothermal compressibility of PVAc.