Objective To evaluate the clinical value of detecting serum underglycosylated IgA1 in diagnosis and differentiation of lgA nephropathy (IgAN). Methods Serum underglycosylated IgA1 was isolated by microspincolumn coupled with vicia villosa lectin (VVL) from 48 cases with IgAN and 43 cases with other primary glomemlonephritis. All the patients were diagnosed by renal biopsy. Sera from 20 healthy persons were used as control group. After isolation, the eluant with rich underglycosylated lgAl was detected by incubation with biotin- labeled horseradish peroxidase (HRP) and Helix aspersa (HAA, recognizing N-acetylgalactosamine specifically)in enzyme-linked immunosorbent assay (ELISA). The sensitivity and specificity of diagnosis and differentiation of IgAN with elevated serum underglycosylated IgA1 were analyzed. Results The level of serum underglycosylated IgA1 in IgAN patients [(83.7±41.0) U] was significantly higher than that in healthy control group [(52.6±22.9) U] and the patients with other primary glomerular diseases[(49.2±27.3) U] (all P<0.01). Twenty-two cases of non-IgA mesangial proliferative glomerulonephritis accounted for 51% of other primary glomerular disease, whose underglycosylated IgA1 level [(47.6±21.5 ) U] (all P<0.01 ) was significantly lower as compared to IgAN patients. Taking the renal biopsy diagnosis as golden diagnostic criteria, the ROC curve was performed. The area under the curve was 0.797 with a standard error 0.047 (P<0.01). The sensitivity as a diagnostic test was 72.9%, with specificity 72.1% and accuracy 72.5%. Conclusion Detection of serum underglycosylated lgAl level by mierospineolumn method and ELISA assay has certain clinical value in diagnosis and differentiation of IgAN.