Financial planning is very imperative in public and private sectors performance not only for developed countries but in developing countries. Tanzania like other developing countries where by public sectors performance is not achieved well. The study examined the effectiveness of financial planning on public sectors 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 staffs from five public sectors in Tanzania through questionnaires. Probability sampling was employed to choose staffs. This study opted mixed research approach. This study opted descriptive analysis such as standard deviation, mean and variance. Furthermore, correlation and multiple linear regression model was 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 be increase the oversights to in order to ensure that the financial planning’s are implemented effectively and efficiently, therefore to archive the public sectors performance in Tanzania. The study likewise suggests that all public sector organizations should make sure that the operation systems are implemented effectively, therefore can archive the performance. Also, the study suggests that financial strategies and full accountabilities from staffs is needed in public sector organizations in order to increase performance.