The refrigerant and oil mixture is known as real working fluid in a vaporcompression refrigeration system. However, in the design of a refrigeration system only the thermophysical properties of pure refrigerants are considered, and the effect of the presence of compressor oil is not taken into account.In order to optimize the refrigeration system, thermophysical properties of refrigerant and oil mixture are required.For this purpose, the viscosity and density for solutions of natural refrigerant isobutane(R600a)with commercial mineral compressor oil SUNISO 3GS were measured at five nominal mass fractions of w(R600a〖DK〗)=100%,95%,90%,85%, and 80% over the temperature range from 253 K to 333 K.The two properties were measured simultaneously using a vibratingwire instrument operated in the forced mode of oscillation.The temperature uncertainty was estimated to be within ±10 mK.The overall uncertainties of these results are ±2.0% in viscosity and ±0.2% in density.The viscosity data were correlated with an empirical approach based on the classical Eyring equation.The measurements of density were correlated with a polynomial as a function of temperature.The maximum and the average absolute deviations of the viscosity measurements from the correlation are 5.73% and 1.75% respectively.With regard to density, the maximum and the average absolute deviations of the results from