The specific volume change of polymer occurs to various reactions of mechanical stress, chemical reaction, glass transition and crystallization and so on. In regular state, the specific volume of material as function of temperature and pressure is changed. The experimental and theoretical equations of state (EOS) are Tait equation and Simha-Somcynsky equation for amorphous polymer and Simha-Jain theory for crystalline polymer. This study carried out measurement of the specific volume as function of temperature and pressure using Gnomix pressure-volume-temperature (PVT) and the measured data were fitted two domain Tait equation. These results that the difference of the measured and calculated value were almost same less than 0.1% and 10 parameters which were obtained Tait fitting use to calculate compressibility and volumetric expansivity of amorphous polymers. The used ABS resins were same butadiene rubber content at 16 wt% but they had different rubber size. ABS1 consisted of only one rubber size and ABS2 consisted of two rubber sizes. The compressibility and volumetric expansivity of ABS1 was higher than those of BS2. However, for the difference of volumetric expansivity between 0 and 100 MPa, ABS2 was slightly lower than ABS1.