In the current study, for finding the optimum GAS process conditions, the liquid-phase volume expansion and process conditions were evaluated for the binary [carbon dioxide (CO2)-dimethyl sulfoxide (DMSO)] and ternary [CO2-DMSO-Capecitabine (CPT)] systems, respectively. To this end, CO2, DMSO, and CPT were considered as the anti-solvent gas, organic solvent, and solute, respectively. The minimum GAS operational pressure (P-min) for precipitation of CPT nanoparticles in the (CO2-DMSO-CPT) system was calculated by Peng-Robinson (PR-EoS) and Soave-Redlich Kowang (SRK-EoS) with conventional quadratic mixing rules (vdW2). The obtained P-min values according to PR-EoS and SRK-EoS at 308, 318, 328 and 338 K were 7.80, 8.57, 9.78 and 10.46 MPa, and 7.27, 7.61, 7.95 and 8.13 MPa, respectively. Also, the mole fraction of CO2, DMSO and CPT in the liquid phase was determined at mentioned temperatures, using PR-EoS. For validation of these models, the P-min values for the [CO2-DMSO-Ampicillin (AMP)] system was calculated at 308, 318, 328 and 338 K by both of models (PR-EoS and SRK-EoS) and compared with obtained results by Ghoreishi et al. for this ternary system. The computed P-min values for precipitation of AMP nanoparticles in the (CO2-DMSO-AMP) system in this work were well in agreement with reported values in the literature. [GRAPHICS] .