In this paper, a genetic algorithm (GA) and constriction factor based particle swarm optimization technique are proposed for solving the short term fixed head hydrothermal scheduling problem with transmission line losses. The performance efficiency of the proposed techniques is demonstrated on hydrothermal test system comprising of three thermal units and one hydro power plant. A wide range of thermal and hydraulic constraints such as real power balance constraint, minimum and maximum limits of thermal and hydro units, water availability limit and discharge rate limits are taken into account. The simulation results obtained from the constriction factor based particle swarm optimization technique are compared with the outcomes obtained from the genetic algorithm to reveal the validity and verify the feasibility of the proposed methods. The test results show that the constriction factor based particle swarm optimization approach give the same solution as obtained by genetic algorithm but the computation time of the constriction factor based particle swarm optimization method is less than genetic algorithm.