This action research aims to develop the scientific explanation of grade 10 students using sociobiological case-based learning on the topic "immune system". The target group consisted of 2 1students who are studying in biology course. The research instruments were: plan of instrument using sociobiological case-based learning, scientific explanation test, student behavior observation, semi-structure interviews, and student journal writing. The data were analyzed by percentage, mean, and standard deviation. The results showed in the first cycle, 18 students received an average scientific explanation score of 9.62 out of a total 12 points, representing 80.16%, and three students did not meet the good level criterion. In the second cycle, 21 students received an average scientific explanation score of 10.90 out of a total of 12 points, representing 90.87% of those who met the good criteria.