The purpose of this study is to design a digital game design-based STEM activity for fifth-grade students learning about endangered organisms and significance of biodiversity for living. This activity was carried out with twenty students in a public school in Eastern Black Sea Region of Turkey during academic year of 2018-2019 spring term. This study planned as eight-lesson time (8 × 40 minutes) and completed at this lesson time. The students were given the digital game design challenge in real-life problem context that has been created based on design-based science learning and for which they shall use their knowledge and skills in each of the STEM disciplines. During this design challenge, students worked like a scientist and an engineer. They carried out scientific research and inquiry process in the science discipline, understood the engineering design process in the engineering discipline, established mathematical relations in the mathematics discipline, learned how to make coding in the technology discipline, and used this knowledge and skills thus acquired in their suggested solutions for the design challenge. They designed a digital game by coding and presented science knowledge and skills that acquired from inquiry process.