This study consists of two models. Model one is conducted to check if there is a target adjustment toward optimal capital structure, in the context of Turkish firm listed on the stock market, over the period 2003-2014. Model 2 captures the interaction between firm size, profitability, market value and capital structure using the moderation mediation model. The results of model 1 have shown that there is a partial adjustment of the capital structure to reach target levels. The results of model 2 have shown that profitably affects market value through two paths. The first one is direct while the other is indirect mediated by capital structure. All paths had significant firm size moderation effect. The magnitude of the direct was notably higher than indirect path. Keywords: capital structure, mediation moderation, Turkish firms, profitability