Environmental conservation understanding is one of the crucial factors which determines student attitudes and behavior towards the environment. This study aimed to investigate the effects of problem-based learning and naturalist intelligence on the students' understanding of environmental conservation. This experimental research was conducted at Madrasah Aliyah Negeri (MAN) 1 Praya which employed factorial design. The first factor was the levels of naturalist intelligence (high and low) and the second factor was learning forms (problem-based and expository learning). Two groups were randomly selected from X-MIPA graders of MAN 1 Praya. The data were collected through tests which then were analyzed using ANOVA at 0.05 significance level. The results of the study indicated that problem-based learning affected the students' understanding of environmental conservation, while naturalist intelligence did not affect it. Furthermore, there were no interaction between these two factors.