Background: Systemic lupus erythematosus (SLE) is an inflammatory, multisystem autoimmune disorder characterized by a multitude of autoantibody production and immune complex deposition, causing damage to multiple organs. Dysfunction of T and B cells are believed to be essential factors involved in the disease pathogenesis. A lack or defect in Treg function is generally considered to support SLE pathology. Aim: Our study aimed to assess CD4+ CD25+ Foxp3+ T regulatory cellspercentage in SLE patients and its relation to activity index and damage index. Methods: 50 SLE patients and 50 controls were enrolled in the study. Flowcytometric determination of peripheral Treg cells was done for all participants. Disease activity was measured using the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI -2k) while disease damage was measured using the Systemic Lupus international collaborating clinics American College of Rheumatology Damage Index (SLICC/ACR DI) which were correlated with T regulatory cells percentage in cases only. Results: Treg cells percentage was significantly decreased in SLE patients when compared with healthy controls (0.1% to 0.9% vs 0.9% to 2.1%) (p< 0.001).As regard SLEDAI -2k, there was a negative correlation between Treg cells percentile and SLEDAI-2k (p< 0.001). Also there was a negative correlation between Treg cells percentile and damage index (SLICC/ACR DI) (p< 0.001). Regarding the correlation between SLEDAI -2K with damage index (SLICC/ACR DI), we found highly significant positive correlation (p< 0.001). Conclusion: Our study showed that Tregs percentile were significantly lower in SLE patients when compared with healthy controls.Treg cells % have significant association with SLEDAI and damage index suggesting the value of Tregs as activity biomarker and marker of damage.