This paper proposes a method of solving transmission network expansion problem using LP-Based Particle Swarm Optimization. An optimal expansion plan for the existing transmission network is proposed. It formulates the design requirements of network planning as an operational planning model and is solved by an optimization algorithm such that an optimal planning scheme is obtained satisfying all constraints. Particle Swarm Optimization is a population- based search algorithm. The experimental results for linear programming technique, LP-based PSO and DC model are given. © 2006 IEEE.