The simplified PC-SAFT equation of state (von Solms et al. Ind. Eng. Chem. Res. 2003, 42, 1098) has been applied to the pure-component properties and vapor-liquid equilibria of mixtures of polyamide 6 with several solvents (water, caprolactam, ethyl benzene, and toluene). These systems are of interest in the design of polyamide 6 manufacturing. The optimum binary interaction parameters between polyamide 6, epsilon-caprolactam, and water are estimated on the basis of experimental pressure data from the respective binary mixtures. The obtained parameters are used for the prediction and correlation of the ternary mixture of polyamide 6, epsilon-caprolactam, and water. In the optimization of the pure-component parameters of polyamide 6, those of epsilon-caprolactam were taken as initial estimates, and only the sigma parameter was further fitted to experimental liquid volume data over a wide temperature and pressure range. Furthermore, the densities of several polyamides as a function of temperature and pressure are successfully correlated by fitting only the sigma parameter determined on the basis of experimental liquid density data. The results show that the simplified PC-SAFT equation of state is a versatile tool for the modeling of multicomponent polyamide systems.