The rapid developments in biotechnology and its implications raise moral dilemmas for individuals and society. Therefore, bioethics education at all levels is necessary. Science teachers should inculcate moral values and ethics among students. However, studies on various aspects of curriculum-oriented moral education remain lacking, despite the growing focus on the prosocial and moral development of students. Moreover, most existing studies have not evaluated the effectiveness of moral education curricula in terms of both students' learning experiences and their learning results. In this light, the present study examined the growth of students' moral reasoning on the moral dilemmas of modern biotechnology applications. A total of 206 high school students participated in the study. They were randomly assigned to a bioethical enrichment module (n1 = 87) and an ordinary case-based module (n2 = 119). We compared the mean of moral reasoning scores before and after implementing the interventions between the two groups. The results showed that the means of the intervention group were higher than those of the ordinary group. Our intervention which integrated not only SSI-based teaching but also synthesized essential features of teaching bioethics explicitly could improve students' moral reasoning scores. The pedagogical implications were also discussed.