Background: The study examined the association between sedentary behavior and self-rated health-related quality of life (HRQoL) in a sample of patients with multimorbidity in Singapore recruited from a primary care clinic. Methods: Sedentary behavior and physical activity were assessed with the International Physical Activity Questionnaire short form (IPAQ-SF). HRQoL was assessed with EuroQol-5 Dimension (EQ-5D) utility index, visual analogue scale (EQ-VAS) and its 5 subscales (Mobility, Self-care, Usual Activities, Pain/Discomfort, and Anxiety/Depression). Depression was assessed via Patient Health Questionnaire (PHQ-9). Logistic and linear regression analyses adjusting for the effect of physical activity, depression, and sociodemographic variables (i.e., age, gender, ethnicity, education) were conducted. Results: 932 patients participated in the study (mean age:64.5 +/- 8.5 years, range: 35-80) and 55% were men. Results indicated that women were less likely to have sedentary behavior (>= 7 hrs/day) than men. Results indicated sedentary behavior was associated with lower EQ-5D index scores, but not EQ-VAS scores. Participants who were sedentary for >= 7 hrs/day were more likely to endorse having problems with mobility, self-care, and usual activities, but not with pain/discomfort, nor anxiety/depression. Conclusion: Sedentary behavior was associated with poorer HRQoL. There is a need for interventions and health promotions to reduce sedentary behavior in patients with multimorbidity.