Abstract: The Central Bank of Nigeria reported that the backward development in Nigeria was attributable to weaknesses in the internal control systems of the banks. This has clearly pointed out the picture of how fraud has been penetrated in the financial strength of Nigerian Banks. In a nut-shell, the damage which this menace, called fraud has done to the banks is innumerable and needs urgent attention. Therefore, the attempt to put an end to this economic degradation, gave rise to the topic of this research study the impact of internal control in the banking sector in Nigeria with Wema Bank of Nigeria PLC as a case study. However, this study is aimed at verifying the conception that an effective and efficient internal control system is the best control measure for preventing and detecting fraud, especially in the banking sector. Data captured for this study, were analyzed through descriptive and inferential statistical methods. The descriptive analysis involves the use of percentages, tabulation and graphical presentation. While the inferential statistical method involved the use of the chi-square. The functions of fraud prevention, detection and control are interwoven, as the three works together to eliminate fraud and fraudulent tendencies. Therefore, internal control is highly significant in fraud detection and preventions in banking sector in Nigeria.