The study aimed to examine the effects of design-based STEM activities developed for renewable energy sources on science teacher candidates' perceptions, attitudes, and behavioral orientations. The one-group pretest-posttest design was used. The participants comprised 40 second-grade teacher candidates studying at a public university, and the study lasted for 14 weeks. The data were collected using a renewable energy perception scale, renewable energy sources attitude scale, sustainable consumption behavior scale, and STEM product-performance observation form. The results demonstrated that design-based STEM activities towards renewable energy sources enhanced teacher candidates' perception, attitude, and behavior toward renewable energy sources. However, there was no statistically significant increase in the unneeded consumption sub-dimension of the sustainable consumption behavior scale and the renewable energy-environment relationship sub-dimension of the renewable energy perception scale.