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Objectives: Proliferative lupus nephritis (LN) is a crucial complication in systemic lupus erythematosus (SLE). This study evaluated the clinical implications of coexistence of membranous LN in proliferative LN in terms of clinical characteristics and long-term outcome. Methods: We retrospectively reviewed the medical records of patients with SLE who underwent renal biopsy between 2005 and 2018. Patients with proliferative LN based on the 2003 International Society of Nephrology/Renal Pathology Society classification were subclassified into pure (Class III or IV only) and mixed (Class III or IV + Class V) proliferative LN. The clinical features at the time of renal biopsy, incidence of end-stage renal disease (ESRD), and all-cause mortality were compared between patients with mixed or pure proliferative LN. Results: Of the 171 patients, 30 and 141 were classified into mixed and pure proliferative LN groups, respectively. Patients with pure proliferative LN showed higher anti-dsDNA antibody and lower hemoglobin, platelet, and complement 3 levels than patients with mixed proliferative LN. The SLE disease activity index was also higher in patients with pure proliferative LN (p = 0.047). The pure proliferative LN group showed a higher proportion of Class IV and higher histologic activity index scores (p < 0.001 and p = 0.004, respectively). During the follow-up period of 58.3 months, 18 patients developed ESRD and 15 patients died. ESRD was exclusively observed in patients with pure proliferative LN, although the incidence of ESRD was not statistically different (p = 0.055). All-cause mortality was comparable between the two groups. Conclusion: Pure proliferative LN was associated with higher clinical and histological activities and modestly increased risk of ESRD. Active immunosuppressive treatment would be required to control the renal inflammation in patients with proliferative LN, regardless of the coexistence of membranous LN. [ABSTRACT FROM AUTHOR]