Purpose: This study investigates the impact of health literacy and knowledge on undergraduates' mental health and attitude towards help-seeking in public universities in Ekiti State, Nigeria; with gender and age serving as moderating factors. Design/methodology/approach: The study adopted the correlational research design. The population of the study comprised undergraduates in public universities in Ekiti State, Nigeria. In all, 601 undergraduates (with respect to their gender) constituted the study's sample. The instruments used for this study's data collection were the Health Literacy Questionnaire (r = 0.87), Health Knowledge Questionnaire (r = 0.94), Mental Health Questionnaire (r = 0.91) and Attitude towards Help-Seeking Questionnaire (r = 0.84). Data were analysed at a 5% significance level, using the Hayes macro process in SPSS version 26.0. Findings: Findings indicate a direct, positive and significant relationship exists among undergraduates' health literacy, health knowledge, mental health and attitude towards help-seeking. Health literacy significantly impacts undergraduates' mental health and attitude towards help-seeking. Gender (in favour of males) has a significant moderating effect on the relationship between health literacy, mental health, and attitude toward help-seeking among undergraduates. Originality/value: Undergraduates' health literacy significantly impacts their mental health and attitude towards help-seeking, with gender having a significant moderating effect. Concerted efforts of governments and health and education stakeholders should be concentrated on creating and promoting health literacy and knowledge as well as mental health and positive help-seeking attitudes among undergraduates with special attention to gender parity, irrespective of age. Future research could focus on this study's concerns for younger learners, especially early childhood as well as the effect of undergraduates' socioeconomic and family status, such as poverty and disabilities, on mental health and attitudes towards help-seeking.