Background: Precise assessment of preoperative mental health and psychological determinants may be useful in identifying patients at risk for poor postoperative outcomes of total knee arthroplasty (TKA). The aim of this study was to investigate the influence of psychological status and physical and mental health on the outcome of patients undergoing TKA. Methods: Fifty-two patients undergoing unilateral TKA were assessed preoperatively with Oxford Happiness Inventory, Eysenck Personality Inventory, 12-item short form health survey (SF-12), and Knee Injury and Osteoarthritis Outcome Score (KOOS) for evaluating depression, personality traits, physical and mental health, and function, respectively. At 1 year after surgery, health-related quality of life (HRQL) and function were assessed using the SF-12 and KOOS. Results: HRQL and function of all personality traits increased significantly after TKA, without significant difference among them. Extroversion and neuroticism did not have significant correlation with subjective well-being, HRQL, and function before and after surgery. Subjective well-being and the baseline physical and mental health scores were correlated strongly and directly with postoperative physical component summary, mental component summary, and KOOS scores and their improvement. Among many factors that significantly affected the outcomes of TKA, the only independent predictor of physical, mental, and functional outcome was depression. Conclusions Outcomes of surgery were not significantly different among diverse personality traits. Patients with less depressive symptoms and higher baseline mental and physical scores had significantly greater improvement in HRQL after surgery. The only independent factor affecting the physical, mental, and functional outcome was depression.