Mental health literacy (MHL) plays an important role in public health. Improving MHL can promote mental health at the individual and public levels. To date, no published studies have assessed the effectiveness of MHL curriculum interventions among undergraduate public health students. The participants in this study were undergraduate public health students (n = 48) who were enrolled in an 18-week MHL curriculum for 100 min per week. MHL was assessed using the Mental Health Literacy Scale for Healthcare Students. A paired sample t-test was performed to examine the immediate and delayed effects of the MHL curriculum. The total MHL score significantly improved, and a moderate effect size was found directly after the intervention and six weeks later. There were significant differences in the recognition of mental illness (p < 0.01), help-seeking efficacy (p < 0.05), and help-seeking attitude (p < 0.05) in the five components of MHL between pre- and post-test. Furthermore, significant improvements were obtained for the maintenance of positive mental health (p < 0.05) and reduction of mental illness stigma (p < 0.001) between the pre-test and follow-up. Our findings provide evidence for the development and implementation of an MHL curriculum for public health education.