Systemic lupus erythematosus (SLE) is a multisystem autoimmune connective tissue disorder characterized by loss of self-tolerance causing immune-mediated tissue destruction and various clinical presentations. Cytokine-mediated immunity involved in the pathogenesis of SLE. Recently, IL-23 was proposed to play a crucial role in mediating tissue inflammation and autoimmunity. The present work was aimed to investigate the relation between levels of IL-23 mRNA and disease activity in patients with SLE and in those with renal involvement. In this work, blood samples from 45 adult patients with SLE and 20 healthy controls were collected. Patients were divided into 3 groups. Group I consisted of 16 patients with active SLE with nephritis. Group II consisted of 13 patients with active SLE without nephritis. Group III consisted of 16 patients with inactive SLE based on the SLE disease activity index (SLEDAI). The IL-23 mRNA relative concentration was detected by Quantitative Reverse transcriptase- polymerase Chain Reaction (RT–PCR). IL-23 mRNA expression level in blood was eleven times higher in SLE patients without activity while in active SLE patients with and without nephritis showed 34 fold and 17 fold higher IL-23 mRNA expression respectively compared to healthy control. IL-23 mRNAs levels were significantly higher in patients with SLE compared with healthy controls (P