In this paper, heat transfer characteristics of hydrocarbon refrigerant R600a-oil mixture during condensation inside a horizontal U-shaped tube are investigated. The experiments are performed in three parts: (i) pure refrigerant flow inside a straight tube, (ii) pure refrigerant flow inside a U-shaped tube, and (iii) refrigerant-oil mixture flow with compactness of 1, 1.5, and 2% inside a U-shaped tube. An experimental setup has a copper tube of 8.7 mm inner diameter as a test condenser which is installed into a polyethylene pipe of 6 cm inner diameter to form a tube-in-tube heat exchanger. The experimental tests are carried out in a wide range of operating conditions, including mass flux of 140–280 kg/m2s, vapor quality of 0.04–0.80, and condensation pressure of 510–630 kPa. The results are validated by comparing the experimental condensation heat transfer coefficient of pure refrigerant flow inside straight tube with well-known empirical correlations. Accordingly, they predict most of the experimental data within ±20% error in pure refrigerant part. The results represent that using a U-shaped tube increases the local and the average heat transfer coefficients by a maximum of 34% and 29.7% in comparison to the straight tube, respectively. In addition, in the presence of oil, the local heat transfer coefficient of refrigerant-oil mixtures increases at low vapor qualities, while decreases at middle and high qualities due to the effect of oil on the condensation liquid film.