Elementary school students frequently struggle to apply causal and scientific reasoning to environmental phenomena, yet elementary science education has not sufficiently integrated evidence-based thinking and contextual learning to address this challenge. However, science instruction at the elementary level remains predominantly focused on memorization-oriented learning, limiting students’ opportunities to develop scientific thinking through authentic investigation activities. This study investigated the development of scientific reasoning and causal reasoning among fifth-grade students through biodiversity learning based on environmental exploration at SD Negeri Tibayan 2, Jatinom, Klaten. The study approach using phenomenological case study design. On this rearch using participans 20 students in five-grade elementary. Data were collected through participatory observation, semi-structured interviews, documentation, and analysis of students’ worksheets and visual representations during environmental exploration activities. The findings revealed that direct environmental exploration supported students’ students’ abilities to identify biodiversity phenomena, construct simple causal relationships, and develop evidence-based scientific explanations derived from empirical observations. Furthermore, exploration activities development the students’ observational skills, ecological awareness, and contextual understanding of environmental relationships. Nevertheless, students’ reasoning patterns remained largely concrete and descriptive, indicating the need for sustained inquiry-based learning to support the development of higher-order scientific reasoning. These findings demonstrate that environmental exploration-based biodiversity learning provides a meaningful pedagogical approach for strengthening scientific reasoning in elementary science education.