Purpose: The purpose of this study was to measure the level of expectations regarding aging (ERA) and identify relationship betweenERA and physical activity of middle aged adults. Methods: Participants were middle aged adults who resided in the community in threecities in Korea. Data were collected using questionnaires that contained items on individual characteristic, International Physical ActivityQuestionnaires (IPAQ), and behavior-specific cognitive factors including ERA-12. Hierarchical multiple regression was conducted to examinewhether ERA would predict physical activity by controlling other factors. Results: The mean age of the participants was 51.1±6.9years. The mean score for ERA (possible range=0 to 100) was 40.04±14.31. More than half of the participants (62.6%) were not engagedin health promoting physical activity. Gender, employment status and exercise confidence were associated with level of physicalactivity (F=7.14, pqqqlt;.001, R²=.36). After controlling for individual factors and behavior-specific cognitive factors, ERA was independentlyrelated to physical activity (F=7.19, pqqqlt;.001, R²=.38). Conclusion: The results demonstrate that individuals’ belief about aging has effectson physical activity in Korean middle aged adults. Thus, nursing interventions which focused on ERA could help enhance physicalactivity in middle aged adults.