Abstarct: This research offers innovative approach in order to optimize the weight of the tapered frxame by using prestressing force.The places of applied prestressing force has been determined in the bottom and top of column. The prestressed cables is one of the practical methods of applying force. Steel tapered frxame has been optimized using Genetics algorithm on the basis of AISC code. In this regard analysis, design and optimization process performed by a code written in visual basic software. Each member of frxame has 5 optimized design parameters including height of web at the ends of member, Thickness of web, Thickness of flange and width of flange.In addition to latter, optimal prestressing force in top and bottom of column is provided by the code. The results of the code in each step including analysis, design and optimization have been verified by comparison with analytical solution and SAP2000 software results. The obtained results indicate the effect of applying prestressing force in tapered frxames. The effectiveness of this method is dependent on the location of applied force and the span of the frxame.