This study examined the administrative challenges on curriculum implementation in public secondary schools in Nyamagana District – Mwanza City, Tanzania. The study was guided by four objectives including: to identify the administrative challenges preventing effective curriculum implementation, to find out the effects of administrative challenges on academic performance, to examine the roles of school heads in ensuring effective curriculum implementation, and to determine possible measures to overcome the administrative challenges facing curriculum implementation in public secondary schools in Nyamagana District. The study was guided by two theories: Administrative Management Theory and The Catalytic or Implementation Theory. The study adopted a convergent parallel design and a sample size of 172 respondents. Questionnaires and interview guide were employed in data collection. Validity and reliability of the instruments were tested and given to the respondents when the two were assured. Descriptive statistics was used to analyze quantitative data with the help of SPSS version 20 while qualitative data was analyzed thematically by creating themes. It was revealed that school administrators face many challenges which lead into their failure to implement the curriculum such as lack of infrastructure, lack of curriculum implementation guidelines, insufficient funds, overcrowded classrooms, heavy workloads, teachers’ lack of commitment, complexity of managing curriculum, and school heads’ inability to supervise curriculum delivery. It is recommended that the Government should provide more funds whenever it rolls out an education innovation so as to enable the schools to effectively implement the innovation. There is also a need to conduct seminars and workshops for school administrators to enable them to effectively implement curriculum innovations in secondary schools.