In this study firm's capital structure decisions have been tried to examine theoretically and empirically. By testing the determinants of capital structure, i.e., size, tangibility, profitability, growth, non-debt tax shield, business risk and liquidity on firm's leverage (capital structure decisions) have been tried to determine. Size, profitability, non-debt tax shield, liquidity and human capital have been found significant and negatively related to capital structure decisions. Our analysis consists of 176 non-financial Pakistani companies listed on Karachi Stock Exchange over the period of 2003-2012.