Critical and creative thinking abilities are part of 21st century skills that have not been well utilized. One effort to improve these abilities can be through project-based learning (PjBL). This quantitative study aims to determine the effect of the PjBL model on students' critical thinking and creative thinking abilities on the ecosystem concept. This research used a quasi-experimental design with the matching posttest-only control group design and a population of all class The sample was determined using a purposive sampling technique with various considerations, selecting class X-1 as the experimental class and class X-2 as the control class. The research instrument used 15 questions for critical thinking skills and 12 questions for creative thinking. The collected data was then analyzed using the one-way ANOVA test. The results of the analysis show that the PjBL model has a significant effect on students' critical and creative thinking abilities on the ecosystem concept (P 0.000 < 0.05). Thus, the PjBL model can be used as an alternative learning to empower 21st century skills.