How does the rationality of the economic agent actually relate to utility?Using unique data from the special surveys of the Korean Labor & IncomePanel Study, this study analyzed the empirical relationship between the two byemploying the strategic thinking ability variables as the proxy of economicrationality and the subjective well-being variables including happiness as theproxy of utility. The results showed that the higher the introspective strategicthinking ability that optimizes individual behavior based on the belief in otherpeople’s rationality, the higher the subjective well-being. The correlationbetween the two is found to be explained by non-economic factors includingsocial relations such as sociability and reciprocity, and self efficacy and selfcontrol, not by economic factors such as income and working hours. Thisfinding suggests that people’s pro-social behavior as a social animal may not bein conflict with the rationality of homo economicus who maximizes utility.