The aim of the present research is to reveal the effects of preservice science teachers' E[right arrow]STEM approach-based activity development processes on their environmental awareness levels and their views on the process. The research was performed with explanatory sequential mixed design. In the quantitative dimension, a single group pre-test post-test quasi-experimental design; and in the qualitative dimension, a holistic single case design, a type of case study, was applied. Eleven preservice science teachers studying in the 3rd grade of the faculty of education at a state university based in the Western Black Sea Region of Turkey are included as the study group. The quantitative data obtained after the six-week process were gathered through the environmental awareness scale and the Wilcoxon signed-row test, and the qualitative data were collected through a semi-structured interview form and analyzed descriptively. It was determined that the activity development process based on the E[right arrow]STEM approach increased in the environmental awareness levels of the preservice teachers and their opinions were positive for the process they experienced. They established connections that the E[right arrow]STEM approach provided the development of environmental awareness and was an effective application area in environmental education. Suggestions were made based on the results of the research. Based on the changes resulted by the E[right arrow]STEM approach activity development process experience in preservice teachers, it was suggested to enrich the content of teacher education and science courses with this approach.