Equation of state for ethane-propane mixture has been made as a combination of Helmholtz free energy of mixture components and the components interaction function. Coefficients of the equation have been determined on the base of experimental data on mixture’s density at temperatures from 195 K to 400 K and at pressure up to 34,6 MPa including the conditions of phase equilibrium. The thermodynamic behavior of mixture at saturation state has been analyzed. It has been stated that the difference of temperatures of saturated vapor and liquid on isobars for different compositions reach 20 K. The refrigerating coefficient values and cold-productivity specific volume of the one-step refrigerating machine cycle using the ethane-propane mixture as a working body have been calculated.