Physics learning in senior high school faces challenges in developing students' scientific reasoning ability. This study aims to examine students' scientific reasoning ability through project-based learning of briquette making and its effect on improving students' critical thinking ability, especially in SMA Negeri 1 Jatiroto, to improve a more effective understanding of physics. The research was conducted at SMA Negeri 1 Jatiroto, Lumajang Regency, in semester one of the 2024/2025 scholastic year. The population of the research sample was class X students, which was determined using homogeneity test and random sampling technique or purposive sampling. The research design used Quasi Experimental with pre-test and post-test. Data collection was done through tests, observations, interviews, and documentation. The pre-test and post-test results showed a significant increase in the experimental class, with a higher mean post-test result (84) than the control class (50). Data analysis displayed a significant difference between the two groups, indicating that the project-based learning model had a beneficial effect on enhancing performance students' scientific reasoning skills. Thus, project-based learning in briquette making is proven to be able to encourage increased understanding of physics concepts while developing students' critical thinking skills more effectively.