This study examined the effect size of professional development programs on teachers' science teaching by meta-analysis method. For this purpose, literature review was made on existing national and international studies. In this context, master's thesis, doctoral dissertation, and articles conducted between 1990 and 2019 were appropriate for the research problem and had statistical data to be included in the meta-analysis study were reviewed and investigated in Turkish and English from national and international databases. As a result of the literature review, 1072 national and international related studies were reached. Among these studies, it was determined that 14 studies (N=969) met the inclusion criteria. The effect sizes and the combined effect size of the studies were calculated using "Comprehensive Meta-Analysis v2.0 (CMA) Statistical Package Program". In the studies combined with random effects in the model, the effect size of professional development programs on teachers' self-efficacy beliefs in science teaching was found to be "moderate". As a result of the heterogeneity test, the study was found to have a high level of heterogeneity. Moderator analysis was performed in order to determine the sources of high levels of heterogeneity between studies. As a result of the ANOVA similarity analysis conducted for the publication type and branch categorical moderators, it was determined that the effect sizes of teachers' science teaching self-efficacy beliefs differed significantly according to the branch variable. As a result of the meta-regression analysis conducted for publication year, sample size, and application period, which were assessed as continuous variables, it was found that publication year and sample size as moderators caused significant differences in the effect sizes of science education teachers' self-efficacy beliefs. Teacher professional development programs were found to have a positive influence on science education teachers' self-efficacy beliefs, and teachers were suggested to be encouraged to participate in such programs.