The banking sector in different parts of the world have challenges in detecting and preventing frauds due to weak controls. However, an effective system if well implemented an organization is capable of preventing and detecting fraudulent activities. The main purpose of this study was to evaluate the effect of internal control system on detection and prevention of frauds in banking sector in Kenya a case of Consolidated Bank of Kenya Ltd. This study was anchored under Attribution theory. The study adopted qualitative and quantitative methods, which assisted in collecting and analysing the data. This study also adopted a descriptive research design to investigate the study variables. Mean, percentages, frequencies and standard deviation were used in descriptive statistics analysis and inferential regression such as multiple regression and correlation were applied to analyse the relationship between the study variable and the significant of the variables respectively. The study targeted a population of 130 staff grouped in 4 subgroups. The outcomes of the research demonstrated that risk assessment had a positive and substantial link with fraud detection and prevention. According to the report, new techniques of improving fraud detection and prevention should be devised, and government rules should be reviewed. Additional study should be done using a cross-sectional research design that includes a questionnaire, an interview, and a secondary data schedule.