This study assessed the factors affecting teacher’s promotion in private schools in West "B" District in Zanzibar. Specific objectives are to assess the criteria used by school administration in teachers’ promotion in private schools in Zanzibar, to identify social factors affecting teachers’ promotion in private schools in Zanzibar, to explore managerial factors affecting teachers’ promotion in private schools in Zanzibar. Along this, the study adopted mixed approach using case study design. 178 respondents were selected as a sample size drawn from the study population. In this study, data were collected through questionnaire and interview as a method of gathering information and analysed by using content analysis technique and Software Package for Social Science (SPSS). The findings of this study revealed that, successful organisation largely values the role of its employees through promoting and the procedures must be properly implemented to avoid the negative attitudes among employees towards the organization. The study recommended that, there should be designed a specific department dealing with the promotions of private schools and to minimize bureaucracy in the promotion process in order to reduce the time to process teacher’s promotions, also the study add that the organization of private schools should have a special fund allocated separately and adequately for promotion of private school’s teachers.