The purpose of this research is to examine the relationship between market structure and performance in the banking sector using data from Pakistani commercial banks. Investigating the effect of changes in the market structure on profitability is based on the structure-conduct-performance (SCP) and efficient-structure (E-S) hypotheses. Researcher has taken a sample of 20 scheduled commercial banks incorporated in Pakistan to examine the above hypotheses, using the annual and panel data for a period of 9 years from year 1996-2004. Three measures of bank's performance are utilized i.e. return on assets (ROA), return on capital (ROC) and return on equity (ROE). Concentration ratio (CR) has been used to measure structure-conduct-performance (SCP) hypothesis and market share to measure efficient-structure (E-S) hypothesis. Control variables were used to capture market specific characteristics such as bank size, market size, risk to owners, liquidity measure,market risk, and market growth as well.