This Paper proposes a new hybrid algorithm for solving the Unit Commitment problem in Hydrothermal Power System using a hybrid Evolutionary Programming - Simulated Annealing method with cooling-banking constraints. The main objective of this project is to find the generation scheduling by committing the generating units such that the total operating cost can be minimized by satisfying both the forecasted load demand and various operating constraints of the generating units. Simulated Annealing (SA) is a powerful optimization procedure that has been successfully applied to a number of combinatorial optimization problems. It avoids entrapment at local optimum by maintaining a short term memory of recently obtained solutions. Numerical results are shown comparing the cost solutions and computation time obtained by using the proposed hybrid method than conventional methods like Dynamic Programming, Lagrangian Relaxation.