This study contributes to a better empirical understanding of the factors that underlie sustainable consumption behaviors with respect to social-cognitive viewpoint. By involving a survey of Korean and Japanese respondents’ awareness, descriptive norm, practical behavior to 47 specific activities, as well as attitude and pro-environmental self-identity, the study works on two levels: on one level, it is a study of sustainability-related consumer activities and behaviors in Korea and Japan; on another level, it identifies key variables to explain sustainable consumption behavior through hierarchical regression analysis. The results show that among the numerous sectors requiring prioritized expansion of sustainable consumption, the area of consumer citizenship has received relatively little publicity. Another important finding is that the failure to practically engage in sustainability-related activities by consumers cannot simply be attributed to knowledge deficit, as consumers in both countries appropriately recognize sustainable consumption. The results clearly illustrate that consumers perform sustainable consumption behavior based mostly on socially shared connotations—the descriptive norm—while the other key variables affecting sustainable consumption are awareness, and pro-environmental self-identity. However, it is also observed that there is no significant effect on attitude, indicating that even a favorable attitude toward performing sustainability-related activities does not directly translate into actual behavior. This paper shows how consumer perceptions of the normality of environmentally friendly behaviors can be used for the design of strategies to promote sustainable consumption in Korean and Japanese societies. In addition, this paper provides the practical guidelines for the expansion of sustainable consumption tailored for the characteristics of each society.