This Study Aimed To Investigate The Effect Of Product Market Competition On The Capital Structure Of Listed Companies In Tehran Stock Exchange (TSE) Since 2005 To 2015, In Today's Highly Competitive And Sensitive Environment. Independent Variable In This Study Is The Product Competitiveness Level In The Market And The Dependent Variable Is The Debt Ratio. In This Research We Measured Product Competition In Market And Its Aspects By Q-Tobin, Market Share, Substitution Goods Ability, Barriers Entry, And Number Of Active Companies. We Used Dynamic Model Data Of Regression (Generalized Method Of Moments) And A Sample Of 87 Companies Selected From Listed Companies In Tehran Stock Exchange (TSE). Our Result Shows That There Are Positive And Significant Relation Between Substitution Goods Ability And Capital Structure Of Listed Companies, Also There Are Negative And Significant Relation Between Two Variables Including Entrances Barriers Entry And Number Of Active Companies In Each Industrial With Capital Structure. There Is No Significant Relation Between Two Variables Including Market Share And Q-Tobin With Capital Structure Of Listed Companies In Tehran Stock Exchange (TSE).