This study was to identify the effect of reflective self-assessment activity and the influence of this in terms of the change processes of University students’ career decision making levels and academic performance. For this purpose, I gathered data from 17(8male, 9female) University students. The data were analyzed through the triangled qualitative approach (group interview, observation, and reflective self- assessment) and quantitative approach for the accurate judgement. In quantitative approach, academic achievement and career decision making levels were conducted before and after the reflective self-assessment and were examined by using the paired sample t-test. During reflective self-assessment, group interview, and observation processes, students had more positive attitudes toward and were more aware of their career decision making, academic performance, thinking, emotional and behavioral processes. Further, students' career decision making levels and their academic achievement were increased significantly. The results of this study supported that reflective self-assessment could be considered as a powerful way and one of the greatest instruments to motivate students, to promote learning like in previous studies. Plus, they suggested the influence of reflective self-assessment.