Proteinuria is a well-known risk factor for the progression of renal dysfunction in chronic kidney disease; however, its importance for estimating the prognosis of lupus nephritis requires verification. Korean adult patients with renal biopsy-diagnosed diffuse proliferative lupus nephritis who had undergone three or more consecutive urine protein to creatinine ratio or urine dipstick tests within six months after renal biopsy were enrolled. The cumulative risks, predictors, and outcomes of proteinuric remission and flare were evaluated. This study included 26 men and 167 women with a mean age at renal biopsy of 31.2 ± 9.8 years. Eighty-two (42.5%) patients experienced proteinuric remission during the follow-up period. During a mean follow-up of 157.9 ± 69.5 months, among patients who achieved proteinuric remission, one died, one developed end-stage renal disease (ESRD), and two had composite outcomes; among patients without remission, nine died, 24 developed ESRD, and 30 had composite outcomes. Patients who achieved proteinuric remission had a 0.089-fold risk (95% CI: 0.011-0.736) of mortality, 0.110-fold risk (95% CI: 0.013-0.904) of incident ESRD, and 0.210-fold risk (95% CI: 0.048-0.920) of a composite outcome compared to patients without remission. Among the 82 patients who achieved proteinuric remission, 59 (72.0%) experienced at least one proteinuria flare; however, relapse did not correlate with the incidence of outcomes. In conclusion, proteinuric remission is an independent predictive prognostic marker of good renal survival and mortality, regardless of the interval from biopsy to remission, recurrence of proteinuria after remission, renal function status at remission, or hematuria remission.