The pressure drop of a capillary tube flow is experimentally investigated. In this study, pure refrigerants such as R32, R125 and R134a and their mixtures such as R32/R134a (30/70 by mass fraction), R32/R125 (60/40), R125/R134a (30/70) and R32/R125/R134a (23/25/52) are used as test fluids. The binary interaction parameters for viscosities of the liquid state of refrigerant mixtures are found based upon the experimental data in the open literature. Several homogeneous flow models predicting the viscosity of two-phase region are compared and Cicchitti’s equation is shown to be the most adequate for adiabatic capillary flows. A model for the prediction of the frictional pressure drop of single and two-phase flow is presented for the refrigerant mixtures in this study.