Inadequate self-directed learning readiness remains a challenge in education. This study examined study habits and mathematical curiosity as determinants of self-directed learning readiness among 185 STEM students. Utilizing diagnostic design, stratified random sampling, survey technique, and multiple regression analysis, it was revealed that only mathematical curiosity manifested a significant contribution, partly and partially supporting Self-Determination Theory. Future research may explore additional factors explaining the remaining 46.9% of the variance in self-directed learning readiness. Educational resources for study habits may be reallocated for the use of developing mathematical curiosity.