Capital structure, dividend policy and corporate governance are today significantly influencing academic debates on firm's value, while they can increase profitability and shareholder's value in long term. This paper seeks to investigate the affects of corporate governance mechanisms and financing activities on firms' performance. A sample of 84 firms listed on Tehran Stock Exchange for a period of five years from 2007 to 2011 was selected. These firms were chosen by employing random classified sampling. The study used Return on Investment (ROI) and Tobin's Q as proxies for performance and developed multiple and single regression models, mean tests and correlation coefficients to test the hypotheses. The findings reveal that corporate governance, financing decisions and capital structures are affected by firms' performance.