OBJECTIVE:Το explore teachers' nutrition knowledge, beliefs, and attitudes and to examine the effectiveness of an electronic learning (e-learning) program in teachers' nutrition knowledge. DESIGN:Cross-sectional and experimental design. SETTING:The study took place in Greece, while schoolteachers were invited by e-mail. PARTICIPANTS:Teachers of primary and secondary education, with no exclusion criteria, were enrolled in the study between March, 2015 and 2016. MAIN OUTCOME MEASURES:Schoolteachers' nutrition knowledge, beliefs, and attitudes. INTERVENTION:Teachers completed a 36-item nutrition questionnaire and then a subgroup participated in an e-learning program. After the intervention, teachers completed the same questionnaire. ANALYSIS:Principal component analysis and multivariate logistic regression were used for data analysis. RESULTS:A total of 1,094 teachers completed the questionnaire; 619 participated in the e-learning program. Teachers showed moderate nutrition knowledge scores (ie, 65% correct answers) before the intervention, whereas their attitudes regarding acting as role models and their belief in the importance of the role of nutrition were associated with 74% (odds ratio, 1.28; 95% confidence interval, 1.13-1.45) and 79% (odds ratio, 1.21; 95% confidence interval, 1.07-1.37) increased possibility of having good nutrition knowledge, respectively. The e-learning program was effective in strengthening teachers' nutrition knowledge (P < .001) and improving their beliefs and attitudes (P < .05). CONCLUSIONS AND IMPLICATIONS:Future research is needed to validate the current results, which can be used to design and implement similar educational programs to teachers as a means of creating health-promoting schools.