The main objective of the study was to investigate the impacts of participatory decision making on the implementation of Tanzania’s secondary school curriculum. The study problem was that, despite the fact that government and private education sector struggled hard to produce and employ many teachers as possible still there a numbers of problems that led ineffective implementation of secondary school curriculum hence poor performance among students in national examinations in Tanzania. This study employed mixed methods research approach in which quantitative and qualitative data collected from 384 respondents. The quantitative data were collected through questionnaires and were analyzed by using SPSS computer program while the interview data were collected from interview and focus group discussion and from documentary review and were analyzed in narrative and content analysis techniques. The findings of this study revealed that participatory decision-making has positive impacts on implementation of the Tanzania’s secondary school curriculum in both private and government secondary schools. The general conclusion of this study is that, participatory decision-making is the notable strategy for effective implementation of the Tanzania’s secondary school curriculum. The general recommendation of this study is that, all heads of government and private secondary schools in Mwanza city advised to revise their leadership styles by practicing participatory leadership model of leadership in order to be effective in the process of implementation of the Tanzania’s secondary school curriculum