Capital structure is one of the most important issues for firms in order to achieve better financial and market performance. The main objective of this study is to examine the relationship between capital structure and firm performance. We investigate 130 manufacturing firms listed on Borsa Istanbul for the period of 2008-2013 using panel data analysis. We utilize short term debt to total asset (STDTA) and long term debt to total asset (LTDTA) as proxies of financial leverage (independent variables). Return on equity (ROE), return on asset (ROA), earnings per share (EPS) and Tobin"s Q ratio were used as proxies of firm performance (dependent variables). Sales growth rate and firm size were used as control variables in the study. We find that STDA has a significant negative relationship with ROA, EPS and Tobin"s Q ratio. Besides, we find that LTDTA has a significant negative relationship with ROE, EPS and Tobin"s Q ratio, while it is positively and significantly correlated with ROA.