The aim of this study was to investigate how mobile outdoor learning supports the development of students' conceptual understanding about local socio-environmental problems and students' attitudes towards the learning activity. To explore these aspects, a study following a design-based research model was designed and conducted with 68 eighth-ninth grade students. The learning design of the activity incorporated a number of mobile learning tools: environmental data collecting devices, tablets and students' smartphones with outdoor learning apps to facilitate the learning activity, which was mainly conducted outdoors. Research data was collected with semi structured pre- and post-questionnaires. The results showed that the students' conceptual understanding about the study topic developed significantly, and they were positively minded about their experience in working on a socio-environmental issue. Based on the results, it can be concluded that mobile outdoor learning activities focusing on timely socio-environmental problems have the potential to increase students' conceptual understanding.