The study investigates residents’ behavior towards reducing the use of single-use plastic (SUP), specifically in the context of food packaging. The widespread view holds that pro-environmental behavior (PB) results from a person’s moral and rational deliberations. In reducing single-use plastic (SUP) consumption and waste, the relative roles of rationality and morality models in validating PB among rural and urban residents are not yet clear. In this empirical study, we compared the relative efficacy of two models for explaining people’s SUP reduction behavior: the theory of planned behavior (TPB; rationality) and the value belief norm (VBN; morality). We investigated Thailand’s rural (Sichang Island) and metropolitan (Nonthaburi city) areas. As a result, we surveyed people living on Sichang Island (n = 255) and in Nonthaburi city (n = 310). We employed structural equation modeling (SEM) for data analysis in this study. Findings showed that while morality better justified all the study participants’ SUP reduction behavior, rationality underpinned behaviors of rural residents, while morality better explained the actions of city residents. We discussed future theoretical development and a policy roadmap based on these findings.