This study evaluated Internal Control System as preventive measure of fraud in the Nigerian banking sector. The objective was to identity whether this has actually achieved the desired result for which it was purposed, especially, in the popular Nigerian banks. To this end, the study was carried out by purposely collecting data from five Nigerian Commercial banks. The data were collected from bank audited and published financial statements and were analyzed with the use of Product Moment Correlation Coefficient and regression analysis. The findings revealed that Internal Control System has significantly prevented and curbed frauds in Nigerian banks. That bad corporate governance was responsible for proper designing of Internal Control System and that Internal Control System has led to increase in the corporate performance of Nigerian banks. Based on the findings, it was recommended that the management of every bank should create and establish a standard Internal Control System, strong enough to stand against the wiles of fraud in order to promote continuity of operations and to ensure the liquidity or solvency and going concern concept of the bank