A new composition-dependent mixing rule in physical contribution term of AEOS by Anderko [A. Anderko, Phase equilibria in aqueous systems from an equation of state based on the chemical approach. Fluid Phase Equilibria, 1991, 65, 89.] was introduced to predict the phase behavior for HFC-134a + HF and HFC-32 + HF binary systems. The approach developed in this work gives better results for systems containing strongly associating compounds in the vapor phase such as hydrogen fluoride than the SRK-based hexamer model developed by Twu et al. [C.H. Twu. J.E. Goon, J.R. Cunningham, A new cubic equation of state for hydrogen fluoride, Fluid Phase Equilibria 1993, 86, 47.] with fewer binary adjustable parameters. The equation of Peng and Robinson [D.Y. Peng, D.B. Robinson, A new two-constant equation of state. Ind. Eng. Chem. Fundam., 1976, 15, 59.] is used to describe the physical interactions. The van der Waals mixing rule was replaced by composition-dependent mixing rules to improve the predictability of this model. This study shows more accurate results for VLE phase behavior for HFC and HF systems than the SRK-based hexamer model or any other activity coefficient-based hexamer models developed so far.