Financial planning is very imperative in public and private sectors performance not only in developed countries but in developing countries. The study examined the effectiveness of financial planning on public sector performance in Tanzania. The performance of organizations was measured by Return on Assets (ROA). The study used the “cross – sectional survey research design”. Data was collected from 128 staff from five public sectors in Tanzania through questionnaires. Probability sampling was employed to choose staffs. This study opted for a mixed research approach. This study opted for descriptive analysis such as standard deviation, mean and variance. Furthermore, correlation and multiple linear regression models were conducted to demonstrate the association between determinants. SPSS application was employed in analysis of data. The results showed that there is statistically positive association between financial planning and public sector performance in Tanzania with P-Value 0.04. The study recommends that the governments should increase the oversight in order to ensure that the financial planning is implemented effectively and efficiently, therefore to archive the public sector’s performance in Tanzania. The study likewise suggests that all public sector organizations should make sure that the operation systems are implemented effectively, therefore can achieve the performance. Also, the study suggests that financial strategies and full accountabilities from staff are needed in public sector organizations in order to increase performance.