Purpose: The purpose of this study was to identify the influencing factors on health related quality of life in middle age. Methods: Data were as collected by self-reported questionnaires from 303 middle age adults. Data analysis was done using SPSS/WIN 17.0 program for descriptive statistics, Pearson correlation coefficients and stepwise multiple regression. Results: The average score of health related quality of life was $79.50{pm}0.40$. Health related quality of life was statistically significant differences according to gender, education, economic status and disease. The health related quality of life was significantly correlated with fatigue, depression, stress, social support, somatic attribution, psychological attribution, normalizing attribution and type D personality. The major factors that affect health related quality of life in middle age were stress, fatigue, type D personality and normalizing attribution, which explained 51.3% of health related quality of life. Conclusion: The findings can provide the basis for the development of nursing interventions to improve health related quality of life. Furthermore, more studies are needed to explore variables that influence on the health related quality of life in middle age.