Economic load dispatch (ELD) problem is one of the most important problems to be solved in the operation and planning of a power system. The main objective of the ELD problem is to determine the optimal schedule of output powers of all generating units so as to meet the required load demand at minimum operating cost while satisfying system equality and inequality constraints. This paper presents a new approach using Particle Swarm Optimization (PSO) for solving the ELD problem with considering the generator constraints, ramp rate limits and transmission line losses. The proposed approach has been evaluated on 26-bus, 6-unit system. The obtained results of the proposed method are compared with those obtained from the conventional lambda iteration method. The results show that the proposed approach is feasible and efficient.