Abstract Background: Tenascin-C (TN-C) is a pro-inflammatory glycoprotein with various biological functions. TN-C plays a major role in cell adhesion, migration, proliferation, and cellular signaling through the induction of pro-inflammatory cytokines. Aim of the Work: This study was designed to investigate the relationship between serum TN-C levels and disease activity in patients with systemic lupus erthromatosus. Subjects and Methods: This is a case–control observational study that was carried out on 68 participants and divided into two groups. Group A included 34 systemic lupus erythematosus (SLE) patients and Group B included (34) apparently healthy volunteers. They were age and sex matched with the patients. Clinical examination as well as routine laboratory investigations confirmed their healthy status. All patients were subjected to full history taking, through clinical examination, laboratory investigations as C-reactive protein, erythrocyte sedimentation rate, C3, C4, ANA, and anti-dsDNA. Serum TN-C estimation of serum TN-C was done for SLE patients and the control group using double-antibody sandwich enzyme-linked immunosorbent assay. Disease activity of SLE patients was assessed according to SLE disease activity index 2000 score. Results: Serum level of TN-C was higher in SLE patients than healthy control but with no statistically significant difference (P > 0.05). There was highly statistically significant difference (P < 0.001) between active and inactive SLE patients regarding TN-C level. Conclusion: Serum TN-C level is elevated in SLE patients and correlates with disease activity which indicates its possible role in SLE pathogenesis. Thus, TN-C may provide a novel research target for the pathogenesis and therapy of SLE