Background: Internet addiction (IA) is associated with mental health problems but its impact on quality of life (QOL) is understudied. We examined the prevalence of IA and its association with QOL in clinically stable patients with major depressive disorder (MDD). Methods: In a cross-sectional survey between September 2020 and July 2021, the Young's Internet Addiction Test (IAT), the Patient Health Questionnaire-2 (PHQ-2) and the World Health Organization Quality of Life Brief version scale (WHOQOL-BREF) were administered to 1267 patients with MDD. Logistic regression was used to examine the correlates of IA, while analysis of covariance (ANCOVA) was used to examine the association between IA and QOL." Results: The prevalence of IA (IAT total scores ≥50) was 27.2 % (95 % CI: 24.7 %–29.6 %) in MDD patients. Compared to patients without IA, those with IA had lower QOL (F = 19.1, P < 0.001). Logistic regression revealed that higher education (senior high school and above; OR = 1.85, 95 % CI: 1.13–3.03), family history of psychiatric disorders (OR = 1.72, 95 % CI: 1.08–2.73), and higher PHQ-2 total score (OR = 1.23, 95 % CI: 1.14–1.32) were positively associated with IA while older age (OR = 0.93, 95 % CI: 0.91–0.96) was inversely related to IA. Conclusion: IA is much more common in clinically stable patients with MDD compared to the reported figures in the general population. It would be prudent to screen and monitor internet use in MDD patients and treat those with IA.