Abstarct: A Special Truss Moment frxame (STMF) is a building framing system that is used for relatively long bay widths. This framing system provides higher lateral stiffness with relatively less weight as compared to sample moment framing systems. Research involving Special Truss Moment frxames (STMF) is of great interest because structures equipped with this system will be able to withstand large seismic events.In this research is done optimization of members cross section and the Values of height and length in special segment of Truss Moment frxames to be the best of seismic performance. Target of optimization is minimize of frxame weight and maximize of frxame behavior factor. In this thesis, behavior factor of Truss Moment frxames is calculated by using Nonlinear Static Analysis and baxsed on standard 2800 with collapse potential(CP) performance level. pushover analysis is a Nonlinear Static Analysis with increscent lateral loads. Optimization constraints Be considered by using design code of Truss Moment frxames Retrieved from AISC360-2005 That are including criterias such as axial force for compression and tensile members, Shear force for Special segment chord members, middle segment truss, Non-special segment chord members and Ratio of The length of each panel to truss beam height. Optimization program is written by matlab programming language and optimization operation is done by genetic algorithm method.