To promote pro-environmental behavior (PEB), it is crucial to understand the drivers behind it. Studies indicate that, in addition to environmental attitudes and nature activities, interest in nature drives people to engage in PEB. However, the relationship between interest in nature and PEB is still greatly understudied among adolescents even though the foundations for PEB seem to be laid during childhood. Therefore, our study focuses specifically on the link between adolescents' interest in nature, their nature activities, and PEB. We collected self-reported cross-sectional data from 954 German school students using the Scale of Interest in Nature (SIN) and the General Ecological Behavior Scale (GEB). Findings indicate a decline in interest in nature, PEB, and nature activities from grade 5 to 9, while also revealing a significant positive correlation between all these constructs. Results highlight the importance of fostering interest in nature in environmental education programs and suggest including it in further research.