Disulfide oil (DSO) mostly burned or stored is known as a low-grade byproduct in gas refining industries. This material is highly perilous to environment. A common way to reduce the environmental impact of DSO is blending in a specific ratio with gas condensate stream in gas refinery. This would improve DSO quality and consequently strengthen its unique application. In this work, density, viscosity and surface tension of DSO and gas condensate mixtures were measured and modeled. Viscosity and density of DSO, gas condensate, and their mixtures were measured in temperature range of 283.15-318.15 K. In addition, surface tension was measured at 298.15 K at different volumetric fractions of DSO-gas condensate mixture. Excess molar volume (V E ), viscosity deviation (Dl), deviation of excess Gibbs free energy (DG E ), and excess surface tension (r E ) were determined based on measured properties. Results showed a positive and negative trend for excess molar volume and excess surface tension, respectively. While fluctuation was observed in viscosity deviation and deviation of excess Gibbs free energy and results showed positive and negative values in different mole fraction. In addition, RedlichKister equation is proposed to predict excess properties of DSO and gas condensate mixtures.Keywords DSO Á Gas condensate Á Excess property Á Viscosity Á Gibbs free energy Á Surface tension