This Study used a panel data of 72 commercial banks located in GCC countries, 28 Islamic banks and 44 conventional banks observed over the period 2007 - 20 II. The aim of the study is to investigate the internal ,and the external factors which influence the GCC banking sectors' profitability, as well as compare between Islamic and conventional banks to see which one is perfonning better in GCC banking sector. This study used regression models that relate bank profitability ratio against eleven explanatory variables which consist of six variables for bank's specific characteristics and five variables for macroeconomic conditions. In this paper, the ratio of return on asset (ROA) and the ratio of return on equity (ROE) were used as proxy of profitability. The results indicate that there are four major internal factors which influence profitability in GCC banking sector. Those four factors are size, bank diversification, capitalization which showed a positive significant influence and credit risk which showed a negative influence on profitability of GCC banking Sector. In tenns of macroeconomic factors, the results show that GCC banking sector was more profitable in pre-crisis period compared to post crisis period. The findings of the paper also revealed that Islamic and conventional banks were similar in terms of the internal factors that influence profitability, except for credit risk, which shows negative significant influence on Islamic banks' profitability. Though, Islamic banks and conventional banks in GCC banking sector had been exposed to similar factors, the comparison study of this paper showed that conventional banks outperfonned the Islamic banks in GCC banking sector. In conclusion, it is wished that this study could provide not only banks manger but also regulators of the central banks in GCC countries, with better comprehension and guideline to promote and enhance the GCC banking sector particularly the financial position of Islamic banks.