Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by autoantibody production, immune complex deposition, and cytokine activation. T-cell immunoglobulin and mucin domain-containing molecule-3 (Tim-3) has a role in many chronic autoimmune diseases by regulating T cell immune responses and Th17/ Treg balance. Tim-3 was found to be elevated in the sera of patients with autoimmune diseases such as SLE. We aimed to quantify the serum levels of Tim-3 in patients with SLE and healthy controls and to investigate the relationship between their serum levels and the disease activity. This casecontrol study was conducted on 85 subjects: 25 participants age and sex-matched apparently healthy controls (group 1), 30 patients with SLE with disease activity (group 2), and 30 patients with SLE without disease activity (group 3). Group 2 was further subdivided into mild, moderate, and severe flare groups according to disease severity. Serum levels of Tim-3 in all groups were measured by ELISA. 2019 EULAR/ACR Classification Criteria for SLE was used to diagnose patients with SLE and SELENA SLEDAI was used to assess the disease activity. There was a highly significant increase in serum levels of Tim-3 in patient group as compared with controls (p<0.001). Also, there was a highly significant increase in serum levels of Tim-3 in group 2 when compared with group 3 and group 1 (p<0.001). There was a negative correlation between serum levels of Tim-3 and WBCs count (r=-0.473, p=0.000), platelets count (r=-0.437, p= 0.000), serum C3 levels (r=-0.503, p=0.000) and serum C4 levels (r=-0.342, p=0.000). Also, there was a positive correlation between serum levels of Tim-3 and 24hour urine protein (r=0.557, p=0.000), presence of RBCs in urine (0.477, p=0.000), presence of pus in urine (r=0.410, p=0.001), ESR (r=0.394, p=0.002) and SELENA SLEDAI score (r=0.643, p=0.000). The area under the ROC curve (AUC) values indicated that the serum levels of Tim-3 was significantly discriminative of SLE patients from healthy controls, AUC