A dissertation submitted in Partial Fulfillment of the Requirements for Award of the Degree of Master of MSc. Accounting and Finance (MSc A&F) of Mzumbe University.Developing a strong system of internal control enables management to deal with rapidly changing economic and competitive environment, priorities and restructuring for future growth. However, the performance of Internal Control systems in organization improves the revenue collection. Specifically, the study was set in order to meet three objectives, namely; to evaluate the current institutional factors affecting revenue collection in ZMC, to study various internal control mechanisms employed by the ZMC to improve revenue collection, and to evaluate the effectiveness of internal control systems employed by ZMC. To achieve these objectives, therefore the study employed a case study as Research Design. The study interviewed 50 respondents using questionnaire and interview guide. To arrive at such respondents, the study employed purposive and convenience sampling methods. In addition, data were analyzed using descriptive Statistics. The findings show that internal controls were available in the organization, and management is committed to the control system performance, and actively segregation of duties, job rotation and supervision of the activities by senior staff are available. Also the study revealed that systems are good enough for the efficiency of revenue collection. In addition to that, it was found that there was compliance of internal controls in relation to the revenue collection through public/private partnership and having responsible parties to monitor the compliance. However it revealed that the internal audit department is not efficient, is understaffed, doesn’t conduct regular audit activities and doesn’t produce regular audit reports although the few reports produced by the internal audit department address weaknesses in the system. It was further revealed that there is continuous shortfall in revenue collection compared to the budget target.