Problem-based learning (PBL) is a pedagogy where students gain knowledge about a subject through solving an ill-structured problem. Critical thinking skills (CTS) are the capacity to think about what to do or what to consider by an individual. This study sought to decide if using Problem-based Learning (PBL) improves the critical thinking skills (CTS) of the students in a secondary school in the subject of economics. This research used an experimental design. Twenty-seven (27) students were purposively selected from a secondary school in Zambales, Philippines for the school year 2017-2018. Results proved that there was a significant difference in the test scores before and after the intervention. We found PBL to be effective in improving the critical thinking skills of the students based on the result of the mean analysis, standard deviation, and t-test. The researchers recommend that problem-based learning may improve the level of critical thinking skills of the students and improve the teaching-learning process.