Objective: Based on the technology acceptance model (TAM), we explored the nationally-bounded roles of four predictors (subjective norms, entertainment, recordability, and networkability) in determining the TAM variables of perceived usefulness (PU), perceived ease of use (PEOU), and behavioral intention (BI) to use diet/fitness apps on smartphones. Participants/methods: College students in the US and South Korea were invited to participate in a survey. We obtained 508 questionnaires (304 from the US and 204 from Korea). Data were analyzed mainly through path analysis. Results: The four factors positively predicted the PU and PEOU of diet/fitness apps. While the effects of the predictors on the three TAM components were generally stronger among the US students than Korean students, the effect of subjective norms on the BI of diet/fitness apps was weaker among Korean students. Conclusion: Findings from the cross-national comparisons were helpful for thoroughly understanding the contextualized mechanisms involved in the adoption of diet/fitness apps.