Background:Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with multi‐organ involvement, among which kidney is one of the most commonly affected organs. Objective: The aim of the present study is to evaluate urinary Angiostatin as a new biomarker for early detection of lupus nephritis and its possible role in predicting disease activity. Subjects and Methods: This was a cross-sectional cohort study conducted on 48 systemic lupus SLE patients; to evaluate whether urinary Angiostatin be a new biomarker for early detection of lupus nephritis. This work carried out on patients in the Nephrology and Immunology Unit of Internal medicine department in Kobri EL Kobba Military Hospital. Subjects included in this study were patients with age group 18-65 years old, of both sexes, diagnosed with systemic lupus erythematosus according to the 1997 American College of Rheumatology (ACR) classification criteria. All persons have been submitted to Full history taking, full clinical examination and Laboratory Investigations as CBC, urine analysis, KFTs, ANA, C3, C4and anti DsDNA. Results: The average age of all patients was (37.3 ± 11.3) years, the average disease duration was (10.46 ± 6.1) years, the average age of onset was (26.25 ± 8.2) years. The average SLEDAI score was (4.4 ± 3.8), and the average SLICC damage index was (1.77 ± 1.34). Regarding gender of the patients, the majority (85.4%) of patients were females; while (14.6%) were males. Regarding renal biopsy data; the mean activity index was (5.06 ± 4.04) and the mean chronicity index was (1.68 ± 1.38).Regarding ISN/RPS class, (18.8%) of patients had class-I nephritis, (47.9%) had class-II nephritis, (16.7%) had class-III nephritis, (14.6%) had class-IV nephritis, and (2.1%) had class-V nephritis. Significant decrease in age and age of onset in active renal group; compared to other groups. Highly significant increase in SLEDAI score in active renal group; compared to other groups. Highly significant increase in ESR and DNA titer, in active renal group; compared to other groups. Significant increase in activity and chronicity index and ISN/RPS class, in active renal group; compared to other groups.SLEDAI score had a highly significant positive correlation with Urinary Angiostatin; with highly significant statistical difference (p < 0.01). Activity and chronicity indices had a highly significant positive correlation with Urinary Angiostatin; with highly significant statistical difference (p < 0.01 respectively). Conclusion: The novel urinary biomarker angiostatin differentiates active renal from active non-renal disease in patients with SLE. The urinary level of this biomarker correlated significantly with SLEDAI, renal SLEDAI and urine protein levels