The study investigated the acts of heads of secondary schools in teacher professional development at Ilala District. The study was descriptive research and survey which employed more qualitative and small quantitative research design. Interview method used to collect data from two heads of school, four heads of department and four subjects teachers. The study employed Adult Learning Theory in analyzing and interpreting data. The findings indicated that the heads of schools had great act and potential contribution in teacher professional development at workplace in public secondary schools. The findings further revealed that the head of school contributed to teacher professional Development through facilitating teachers’ collaboration, supervision, ensuring the using of the availability of teaching and learning resources, sharing of responsibilities, facilitating attendance in workshops and seminars as well as challenges facing heads of secondary school in teacher professional Development. Finally, the study recommends that, as far as heads of secondary schools have crusual act in teacher professional development they are supposed to create green pasture environment for in-door and outside training (in-service training) for teachers to develop professionally.