Background: Urinary biomarkers may help in identification and assessment of the activity of lupus nephritis (LN).Urinary osteoprotegerin may reflect renal disease activity better. Objective: To investigate urinary osteoprotegerin level as a potential marker of lupus nephritis activity. Patients and Methods: The study included 90 individuals classified into three equal groups: Group (I): clinically and laboratory free, Group (II): patients without renal involvement (non active renal group) and Group (III): patients with active lupus nephritis. Measurement of the level of urinary osteoprotegerin has been done by ELISA from January 2018 till June 2019. Results: All patients with systemic lupus erythromatosus SLE in group II and III had significant higher levels in urinary Osteoprotegerin compared to the control group (I). Moreover, SLE patients with lupus nephritis activity (Group III) had marked increase in urinary osteoprotegerin more than SLE patients without renal involvement (Group II).      The study showed also that, with advance of renal histopathological class in lupus nephritis patients, the urine OPG level showed more increase. Conclusion: Urinary level of osteoprotegerin may be used as a biomarker for early prediction of lupus nephritis. Also, it may be used for monitoring the progression and follow up of lupus nephritis as well as with shifting from one class to another.