This observational cohort study evaluated the prognostic value of mast cells in the pathogenesis and progression of IgA nephropathy.A total of 76 adult IgAN patients were enrolled into this study from Jan 2007 and June 2010. Immunohistochemistry and immunofluorescence were used to identify tryptase-positive mast cells in renal biopsy samples. Patients were classified into Tryptasehigh and Tryptaselow groups. Depending on an average of 96-month follow-up, the predictive value of tryptase-positive mast cells in IgAN progression was analyzed.Tryptase-positive mast cells were found frequently in IgAN kidneys while rarely observed in normal kidneys. We also found IgAN patients in Tryptasehigh group presented both severe clinical and pathological renal manifestations. Furthermore, Tryptasehigh group contained more interstitial macrophages and lymphocytes infiltration than Tryptaselow group. Higher tryptase-positive cells density is associated with poor prognosis in patients with IgAN.High renal mast cells density is associated with severe renal lesions and poor prognosis in patients with Immunoglobulin A nephropathy. High renal mast cells density might be used as a predictor of poor prognosis in patients with IgAN.© 2023 S. Karger AG, Basel.