Introduction: Systemic lupus erythematosus (SLE) is an auto immnune connective tissue disorder with a wide range of clinical features, which predominantly affects women. Glomerulonephritis is a major determinant of the course and prognosis of SLE. Complement 1q is the first component of the classical pathway of complement activation. Recently, antiC1q auto antibodies have been proposed as useful marker in SLE since their occurrence correlates with renal involvement and, possibly with nephritic activity. Aim of work: The aim of this study was to investigate the value of anti C1q and its correlation with renal disease in SLE.Patients and methods: This study included 50 patients with SLE and 25 control group. Of the 50 SLE patients, 25 patients with nephritis (Group I) and 25 patients without nephritis (Group II). Database for every patient included full history taking, clinical examination, relevant laboratory tests, immunoprofile including ANA – Anti-dsDNA, anti C1q was tested in the sera of every patient and control group using enzyme immunoassay (EIA)and renal biopsy in lupus nephritis patients. Results: Significant difference was found between the level of antiC1q in all SLE patients and control group (4.8±6.2 mgEq/ml and 1.5±0.2mgEq/ml, respectively, P=0.0001).The comparison between level of anti C1q in group I, group II was statistically significant (12.5+5.4mgEq/ml,4.4+3.9mgEq/ml, respectively, P=0.0001. 6 patients from 25 patients of group II developed nephritis and comparing the level of antiC1q between those 6 patients and rest patients of group II was statistically significant(P=0.02).There was insignificant positive correlation between the level of antiC1q and age of patients, dose of steroids (mg/d), duration of disease ,systolic and diastolic blood pressure and ESR, Platelet count, Creatinine, 24 hr urinary protein and C4 however there was significant positive correlation with SLEDAI (r= 0.5,p= 0.02)and insignificant negative correlation with Hb, WBC and C3(group II) and significant negative correlation with C3 (group I). Statistically significant differences was found between the level of antiC1q in patients with grade II and the level of antiC1q in patients with III and IV (8.2 ± 4.8, 13.6 ± 5.2 respectively, P =0.02). Conclusion: In conclusion, anti C1q is a good biological marker in SLE patients that correlated with renal involvement and is good predictor for development of nephritis.