This study was conducted to develop a model that can predict environmentally friendly purchasing, usage, and disposal behaviors based on environmental knowledge; to empirically analyze the mediating effects of environmental affect among these research constructs; and to provide recommendations for making environmental education, environmentally friendly advertising and public relations, and campaign activities offered by governments and corporations more effective. The findings of this study are summarized as follows. First, higher subjective knowledge about the environment was found to have a direct significant effect on environmentally friendly purchasing and usage behaviors, and an indirect effect on purchasing, usage, and disposal behaviors through environmental affect. Second, higher objective knowledge about the environment was found to have a direct significant effect on environmentally friendly disposal behavior, and an indirect positive effect on purchasing, usage, and disposal behaviors through environmental affect. Third, this study sought to examine not only the direct effects of subjective and objective environmental knowledge on environmentally friendly behavior but also the effects mediated by environmental affect. The analysis results showed that environmental affect had a significant effect on environmentally friendly purchasing, usage, and disposal behaviors. This suggests that environmental knowledge serves as an effective means of managing environmental affect. Therefore, to further enhance the influence of consumers' environmental affect, the findings imply that when developing government environmental campaigns or environmental education programs, and when creating advertisements for corporate green products, it is necessary to emphasize the severity of environmental issues and the benefits of green products in ways that can appeal to consumers' emotions. Ultimately, governments and corporations should consistently and continuously educate consumers through such activities about why environmental conservation is necessary, and furthermore, should encourage the practice of prioritizing environmentally conscious behavior in everyday life.