The importance of ethics education for undergraduate engineering students has been emphasized due to the manifold impacts of engineering on society. However, little is known about moral disengagement among engineering students, which could potentially lead to unethical engineering practice. Especially, it is not known how engineering students’ moral disengagement changes over the course of their college studies. In this paper, we conducted a longitudinal, mixed-methods study to investigate moral disengagement among undergraduate engineering students (n = 274) using Bandura’s theory of (...) moral disengagement as a theoretical framework. We found engineering students’ overall propensity to morally disengage did not change over time, but there were statistically significant differences in student responses to three mechanisms of moral disengagement. We further investigated these findings with students’ interviews. Based on our results, we discuss various theoretical and practical implications. (shrink)