In this study, the heat transfer characteristics of an improved absorber tube of parabolic trough solar collector LS-2 are investigated using ANSYS software. Oil syltherm 800 type is used as a heat transfer fluid. Three types of absorber tubes are tested; the first is a smooth tube and the others are finned tubes. One of the rough cases is rectangular cross-section fins with rounding at fin base and the other does not have rounding at fin base. Simulations are performed with fin thickness variations of 2, 4 and 6 mm. The fin lengths change at 5, 10, 15, 20 and 25 mm. The radii of rounding are 2, 3 and 4 mm and angles between fins are 45° and 90°. Wide range of operating parameters is considered, such as inlet fluid temperatures (300:600 K), flow rate (6:24 m3/h) and direct normal irradiance (500:1000 W/m2). The thermal efficiency, Nusselt number and thermal enhancement index are calculated under different operating conditions. The results show that thermal enhancement index of the fin with round edge radius of 4 mm is higher than that of the fin with the sharp edge (R = 0 mm) by about 10.74% under the considered conditions. The thermal enhancement index of the round edge fins with a length of 25 mm is nearly 25.6% higher than that of the round edge fins with a length of 5 mm. At a fin thickness of 6 mm, the thermal enhancement index of the round edge fin is nearly 7.8% higher than that of the sharp edge fin. At 45° angle and 25-mm fin length, the thermal enhancement index for round and sharp-edged fins is 1.644 and 1.532, respectively. When the inlet fluid temperature increased from 300 to 600 K, the heat enhancement index value increased by 14.57%; as the flow rate increased from 6 to 12 m3/h, the heat enhancement index value decreased by 11.63%. The thermal enhancement index increased from 1.265 to 1.359 as the direct normal irradiance varied from 500 to 700 W/m2.