Critical thinking skills are referred to as one of the 21st-century skills. These skills should be empowered through Biology learning. This study aims to analyze the improvement of biology-critical thinking skills in students who are taught through the CIRC learning model based on the scientific approach (Cirsa). Critical thinking skills are measured by tests developed by researchers and validated by theoretical biologists. The instrument includes indicators of critical thinking skills such as formulating problems, giving arguments, making deductions, conducting inductions, conducting evaluations, and deciding and implementing. This study used a quasi-experimental method with a pretest-posttest non-equivalent control group design. This study involved 160 students (M = 95, F = 65) of 8th grade of a Madrasah Tsanawiyah School in Bogor. The findings of this study show that students who are taught by Cirsa have higher Biology-critical thinking skills than those by conventional learning. In conclusion, Cirsa learning was recommended to develop or enhance students' critical thinking skills related to biological concepts.