SUMMARY
Professional training for in-service teachers is at an utmost level to improve their teaching practices. Therefore, this study aimed to assess the effect of professional training on in-service secondary school physics teachers' motivation to use Problem-Based Learning (PBL). A pre-and posttest quasi-experimental design was used to conduct the study. A two-day professional training on PBL was delivered as an independent variable, while teachers' motivation to use PBL was conceived as the dependent variable. The study involved fifty (50) in-service physics teachers (20 in control and 30 in the experimental group) from 25 secondary schools in four districts of Southwestern Uganda. Data were analyzed with SPSS v.23.0 using descriptive statistics, and paired, and independent samples t-test. The findings indicated a high statistically significant (p<.05) positive change and a greater motivation to use PBL among teachers who received professional training in PBL compared to those who did not receive it. It was recommended that the Government, in conjunction with school administrators, regularly organize similar training and, if possible, for all teachers national wide.https://doi.org/10.26803/ijlter.21.8.16