This research aimed to determine the factors affecting university students' career decision regret. The research was designed as a mixed method research using explanatory sequential mixed design, one of the mixed method designs. The quantitative phase of the research was carried out with 249 undergraduate students studying at Trabzon University Faculty of Education in the 2022-2023 academic year, and the qualitative phase with 5 students selected from this sample group by criterion sampling method. The quantitative data of the study were collected through the "Career Decision Regret Scale" adapted into Turkish by Erdurcan and Kırdök (2017), and the "Personal Information Form" prepared by the researchers, and the qualitative data were collected through semi-structured interviews. According to the quantitative findings, while university students' career decision regret levels differed statistically based on gender and year, there was no statistically significant difference based on department. According to the qualitative findings, it was concluded that 4 main themes, namely occupational, family, environmental and psychological factors, affected the students' career decision regret. The findings obtained from the research were discussed in the light of the literature and some suggestions for future research were presented.