Purpose: To identify the factors influencing Quality of Life (QoL) in rectal cancer patients and to examine whether perceived social support mediates the relationship between defecation function and QoL. Methods: Using self-report questionnaires, a descriptive survey was conducted with 131 rectal cancer patients who underwent anal sphincter-saving resection, in a large medical center in Korea. Data were collected between September and November, 2014, using research instruments validated in the Korean language. The data were analyzed using SPSS/WIN 21.0 and AMOS 21.0. Results: The mean age and post-surgical follow-up period of the participants were 59.0±10.2 years and 15.9±9.8 months, respectively. Multiple linear regression analysis revealed that, after adjusting for age and gender, defecation function, perceived social support, and employment status predicted QoL. Path analysis showed that perceived social support partially mediated the relationship between defecation function and QoL with a significant indirect effect. Conclusion: These results suggest that a positive perception of social support from family and healthcare providers is necessary to improve the QoL of patients experiencing defecation dysfunction after rectal cancer surgery. To this end, periodic counseling and education from outpatient healthcare providers, during the postoperative follow-up period, could encourage patients to perceive higher social support.