The e-commerce market in Vietnam has been developing rapidly in recent years. Understanding customers’ perceived benefits will bring great advantages for businesses. This research develops and validates a scale to measure customers’ perceived mental benefits when shopping on e-commerce sites in Vietnam. The scale is based on the Theory of Planned Behavior, Self-determination Theory, Technology Acceptance Model, Learning and Constructivism Theory, Theory of Privacy, and Persuasive Communication Theory. The mixed-method is applied using both qualitative methods (in-depth interview, focus group discussion) and a quantitative method (questionnaire survey with 917 respondents). The results indicate that the perceived mental benefit is a second-order factor of five dimensions (perceived shopping enjoyment, perceived social interaction, perceived discreet, perceived control and perceived credibility) with 23 variables. Based on the survey of knowledgeable respondents using e-commerce, the analysis results show that this scale ensures validity, reliability, unidimensionality and convergent validity. The managerial implications and suggestions for future research are also discussed.