Background: Complement activation has an important role in the pathogenesis of IgA nephropathy. Objective: To determine the correlation between IgAC3 ratio (IgA/C3) and total Oxford score and predictive value of IgA/C3 in IgA nephropathy. Methods Forty-three patients diagnosed with IgA nephropathy with > 10 glomerular + 1 arteries in biopsy were included in the study. Hematological and biochemical variables of the blood sample taken before the biopsy and total Oxford score were recorded. The study group was divided into two groups as proteinuria ≥ 1 g (PU ≥ 1) and proteinuria < 1 g (PU < 1). Statistics were carried out with SPSS 22.0 program. p <.05 considered as significant. Results: The mean age of 43 patients was 40.4 (± 11.9) years; 51.2% of them were women. Proteinuria as 1 g or more was in 27 of 43 patients, and less than 1 g in 16 patients. The serum C3 level was lower in the group with PU ≥ 1 and showed a significant positive correlation with the IgA/C3 total Oxford score. Conclusion: A significant correlation was found between serum IgA/C3 and total Oxford score.