We explored the factors affecting green purchase behavior among South Korean consumers, with a special focus on the role of knowledge. A structural equations model was tested with 533 respondents and the results indicated that knowledge was a powerful factor to facilitate Korean consumers’ green purchase behavior and that the roles of objective and subjective knowledge were different in shaping green purchase behavior. Subjective knowledge had a direct effect on green purchase behavior and also an indirect effect via green attitude and perceived consumer effectiveness, whereas objective knowledge had only an indirect effect on green purchasing via green attitude and perceived consumer effectiveness. The results indicate that knowledge is a powerful factor in facilitating green purchase behavior, and that ongoing education and publicity should be designed to increase subjective knowledge as well as objective knowledge to be effective for promoting consumers’ green attitude and behavior. © 2018 Scientific Journal Publishers Limited. All Rights Reserved.