Immunoglobulin A nephropathy (IgAN) is characterized by the qualitative abnormality of immunoglobulin A (IgA) in circulation and deposits of IgA in the renal mesangium. Transforming growth factor β1 (TGF-β1) plays a key role in fibrogenesis and the progression of renal damage. This study aimed to investigate the clinicopathologic data on IgAN in northeastern China and the presence of TGF-β1, total IgA, and secretory IgA in the glomeruli and sera, as well as changes in galactose-deficient IgA1 in the serum. We investigated the clinicopathologic data of 1050 cases of IgAN diagnosed in a single center over 13 years. We then assessed the concentrations of TGF-β1 and immunoglobulins in the serum of 100 patients with IgAN and 56 healthy control subjects by enzyme-linked immunosorbent assay, and investigated their presence in the glomeruli by immunofluorescence and reverse transcriptase-polymerase chain reaction. From our data, 76.17% of the IgAN cases belonged to classes I and II according to the World Health Organization classification, representing the early stage. Compared with other studies, we found significantly lower frequencies of segmental glomerulosclerosis (27.71%) but higher frequencies of endocapillary proliferation (50.67%), and a similar proportion of mesangial hypercellularity (68.48%) and tubular atrophy/interstitial fibrosis (moderate, 17.81%; severe, 1.52%) in the northeastern Chinese cohort. There was an increased presence of TGF-β1 and immunoglobulins in the serum and glomeruli of IgAN, which correlates with the progression of pathologic classification. The pathologic variables of the Oxford classification correlated significantly with the WHO classifications. TGF-β1 and immunoglobulins could be used as biomarkers of IgAN pathogenic mechanisms, acting as important adjuncts to the original Oxford Classification.