The quality of education depends on how skilled and motivated teachers are to improve their professional knowledge and skills throughout all their career for sustained performance. In this regard there has been a growing and continuous demand for teachers to improve their knowledge and skills on curriculum and teaching methodology through professional development strategies. However, gaps in teacher's professional development is a worldwide problem. This calls for the development of teachers beyond their initial training. In this regard the study focused on the effect of professional development on teachers' performance. In order to successfully accomplish the objective, the study used an explanatory research methodology. The teachers from 248 public secondary schools were the target demographic. The target population was 2262 teachers from 248 public secondary schools in Uasin Gishu County. Taro Yamane (1967) formula was used to determine the study's sample size of 340 teachers. Data was collected using a questionnaire which was tested for validity and reliability after pre-testing in Nandi County. Data was analysed inferential and descriptive statistics Using SPSS version 20. From the findings formal professional development (t = 12.292, P<.05) and informal professional development (t = 2.075, P<.05), implying that all the professional development strategies significantly affected teachers' performance in public secondary schools in Uasin Gishu County. All the two professional development strategies understudy (informal and formal professional development) jointly explained 56.5 percent variation on teachers' performance. In this regard the public secondary schools should encourage teachers' professional development strategies for maximal teacher performance through a policy framework.