In this work, a hybrid method is developed to identify simultaneously the fluid thermal conductivity and heat capacity for a transient inverse heat transfer problem. The proposed method is a combination of the modified genetic algorithm and Levenberg–Marquardt method. A modified genetic algorithm is adopted for searching the better feasible solution which becomes the initial-guessed solution for starting optimization by the Levenberg–Marquardt method. As the cost function is smaller than a default value, the Levenberg–Marquardt method is employed to speed up the convergence speed. Numerical examples are included to demonstrate the performance of the proposed method. In comparison with the modified genetic algorithm and the Levenberg–Marquardt method, the proposed hybrid method is efficiently converged to yield good estimates.