Purpose: This exploratory study aimed to examine the development of entrepreneurial mind-set among lower secondary school students while undergoing Green STEM project, which integrates the Thinking Based Learning in the 6E Instructional Model as a teaching strategy. Methodology: This study employed fully qualitative approach with one intact class comprising 27 students in one sub urban National Secondary School in Kelantan. The extended period after school time was used for purpose of this study. The students were divided into 5 small groups that work cooperatively to produce a model of Raft using material available in their community. They were guided using Green STEM for eight weeks. The data were obtained through focus group interview after eight weeks. Findings: Analysis of the data showed that the integration of Thinking Based Learning in the 6E Instructional Model as teaching strategy while doing STEM project supported the cultivation of entrepreneurial mind-set among lower secondary students. The entrepreneurial mind-set led students to apply reflective thinking and reasoned decision to solve problems using their creativity and resourcefulness even in a risky and uncertainty environment. Significance: With the success of cultivating entrepreneurial mind-set, integration of Thinking Based Learning in the 6E Instructional Model could inspire the teachers to consider implementing Green STEM project as a part of enriching programme in class room or outside classroom activity.