The main goal of structural optimization is to minimize the weight of structures while satisfying all design requirements imposed by design codes. In this paper, the Modified Simulated Annealing Algorithm (MSAA) is implemented to minimize the weight of truss structures with discrete sizing variables. MSSA is a newly improved version of the simulated annealing (SA) algorithm with three modifications: preliminary exploration, search step and a new probability of acceptance. The reliability of the MSAA is demonstrated through five