In this article, a maiden effective approach named, chemical reaction optimization (CRO) in tuning the proportional-plus-integral (PI) controller is suggested for automatic generation control (AGC) of a two-area hydro thermal power system. The comparison of the optimum values obtained for the PI parameters by the proposed method is compared with that obtained by other population based optimization techniques lke biogeography based optimization (BBO), differential evolution (DE) and genetic algorithm (GA) to show the effectiveness of the proposed method in improving the system performance. The simulation results show that the objective function value keeps on decreasing much faster and gives a better value compared to that obtained by other reported algorithms. This implies that CRO improves the dynamic performance of the system and has better convergence characteristics as compared to the BBO, DE and GA techniques, proving the superiority of the proposed technique.