A Dissertation Submitted in Partial Fulfillment of the Requirements for the Award of Master of Business Administration (MBA-Corporate Management) of Mzumbe UniversityThe study was about assessment of the effectiveness of implementation of open performance review and appraisal system in improving employees‟ performance in public service organizations in Tanzania. Iramba District Council in Singida being the case of the study. The unit of inquiry involved employees of the council which included top management, middle and lower cadre employees. The study sample size was 85 employees out of 285, employees who were obtained through simple random and sampling techniques. The study sample frame was council‟s employees register. Data collection involved the following tools; questionnaires, interviews and observations. Interviews were conducted to collect data from heads of departments while questionnaires and observation were for the employees other than the heads of departments. Data were process and organized in tables and charts, thereafter analyzed using statistical package for social science (SPSS) research Findings show that, the supervisor and the subordinate meet to set and agree on the targets in which the employee‟s performance will be assessed. However supervisors do not give feedback to subordinates, therefore employees may not know where they stand in terms of performance The study reveals that the majority of respondents have a negative attitude towards the performance appraisal while few disagree. Iramba District Council (IDC) should work on these negative perceptions so as to develop the necessary attitude on employees to the performance appraisal by planning to train its management staff, officers and supporting staff and ensure continuous training. Also, the study sought to ascertain whether the OPRAS at IDC is effective in improving employee‟s performance. The study reveals that that majority of respondents see OPRAS as a useful tool for improving organizations‟ performance but some individuals see the process of filling OPRAS as wastage of time. Therefore, to make performance appraisal effective and improve employees‟ performance, IDC should make proper application of a system so that it really serve as a tool of improving individual and organization performance.