In this study, laminar flow is considered, and the heat transfer oil is investigated numerically in horizontal, smooth and micro-fin tubes at different fin heights and spiral angles with boundary conditions of constant wall temperature. The variables considered in the micro-fin tubes are the number of fins that varies from 40 to 60, the micro-fin’ s height that varies is from 0. 2 to 0. 5 mm, and the micro-pin spiral angle that varies between 5 and 47 degrees. This study was conducted for Reynolds number ranging from 500 to 100, inner tube diameter of 8. 62 and outer diameter of 9. 52 mm. The numerical resolution was done using ANSYS fluent v. 15 commercial software. The numerical method was validated by comparing the results of simulating laminar flow of oil through a smooth and micro-fin tube with experimental results and previous observations. The simulation results are then used in the genetic algorithm for optimizing the micro-fin geometry. The results showed that increasing Reynolds number and micro-fin height increases the optimum surface. However, a different trend is observed for the desired spiral angle.