Objective To investigate the relationship between body mass index (BMI) and absolute renal risk (ARR) in IgA nephropathy. Methods The clinical data of 82 patients with IgA nephropathy admitted in our hospital from January 2012 to August 2017 were retrospectively analyzed. The relationship between BMI and ARR was analyzed. Patients were divided into healthy group (18.5 kg / m2 ≤ BMI <24 kg / m2, 38 cases), overweight group (24 kg / m2 ≤ BMI <28 kg / m2, 28 cases) and obese group (BMI≥28 kg / m2, 16 example). Results There were significant differences in sex, age, diabetes mellitus, hypertension, ARR score, serum uric acid, Scr, BUN and Cys C in healthy group, overweight group and obesity group. There were significant differences in renal vascular score between healthy group, overweight group and obese group. There was no significant difference in glomerular score, renal tubulointerstitial score and total score between the two groups. Multivariate and multivariate logistic regression analysis showed that BMI was an independent risk factor for ARR in patients with IgA nephropathy (OR = 1.423, 95% CI: 1.130 ～ 3.736). Conclusion Obesity is a risk factor for elevated ARR in IgA nephropathy, and obesity may indicate poor prognosis.