This paper presents Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) technique to solve dynamic economic dispatch (DED) problem. The main purpose of DED is to minimize total cost of generation power to take care of the various load demand in each hour. DED problem solution also must provide individual inequality and equality constraints at the same time. The algorithms have been applied to two test system, taking into account transmission losses. The first of the selected systems is 3 unit test system and the second is 10 unit system considering the valve point effect. Simulation results applied on the test systems show that the two algorithms obtained optimal and reliable results compared to the other methods used in the literature.