The objectives of this paper are to determine the significant factors that affect the capital structure of listed pharmaceutical firms in Bangladesh and to test the capital structure theories. To achieve the intended objectives a panel dataset including 8 major pharmaceutical firms were taken over the time period from 2009 to 2013. The collected data were analyzed by employing correlated panels corrected standard error model using six variables i.e. profitability, tangibility, growth, size, liquidity and operating leverage. Among the 6 variables tangibility, profitability and operating leverage were found to be statistically significant determinants of capital structure. Profitability, tangibility, growth and operating leverage are negatively related to the capital structure while size and liquidity are positively related to the capital structure of the pharmaceutical firms of Bangladesh. The empirical analysis finds that the static trade-off theory and the pecking order theory are the most dominant capital structure theories for the pharmaceutical firms of Bangladesh. These factors must be considered by the financial manager to determine the appropriate capital structure for the company to maximize value of the firm.