Tanzania is among the developing countries which struggling much to improve service delivery to its people. Since 2004 it introduces OPRAS with the aim to encourage the performance of public servants. This study attempted to examine the effect of open performance review and appraisal system (OPRAS) in assessing teachers in government secondary schools in Bukoba municipality. The study was mixed research approaches that were qualitative and quantitative. Data were collected through questionnaires, unstructured interview and documentary review. It involved 10 government secondary schools, 80 teachers who were systematic selected and purposefully 10 heads of schools selected. The study was guided by four objectives. Generally it founded that both heads of schools and teachers have inadequate training in the implementations of OPRAS form. OPRAS is not the criteria used by the government for the provision of salary increases, promotions or demotions but the government use different criteria’s such as years of working experience and teachers qualifications. The findings show that OPRAS is ineffective in teaching professional because teaching and learning environment is not yet conducive, no enough teaching and learning resources at schools so difficult to achieve academic objectives. The research identifies enough training, provision of feedback for teachers and participation between employer and employees in all decisions making regarding academic issues as the major ways for improving the appraisal system for teachers. The study recommended that, if the government wishes to continue with OPRAS to assess teachers it should provide training for them from its objectives, procedures and its importance.