Background <p>IgA nephropathy (IgAN) is the most common type of primary glomerulonephritis. Elevation in the blood levels of aberrantly glycosylated IgA1 is a crucial initial step in IgAN pathogenesis. Here, we aimed to determine the longitudinal changes in the serum levels of IgA1 <i>O</i>- and <i>N</i>-glycoforms in patients with IgAN receiving different treatments.</p> Methods <p>We enrolled Japanese patients diagnosed with primary IgAN: 10 patients who underwent tonsillectomy and corticosteroid therapy (T-CST), 7 who received corticosteroid therapy (CST), 8 who received conservative therapy (CO), and 5 with other renal diseases who received corticosteroid therapy (ORD) as disease controls. IgA was purified from patient sera collected at diagnosis and post-treatment. After sample preparation, <i>O</i>-glycoforms of the hinge region (HR) and <i>N</i>-glycoforms of the fragment crystallizable region were analyzed using high-resolution mass spectrometry (MS).</p> Results <p>The MS analysis of <i>O</i>-glycoforms of IgA1 showed that the relative abundance of IgA1 with 3GalNAc3Gal, which we previously identified as a characteristic IgA1 <i>O</i>-glycoform in IgAN, decreased post-treatment only in the T-CST group (<i>P</i> = 0.0195). Regarding <i>N</i>-glycoforms, the relative abundance of fucosylated <i>N</i>-glycan at asparagine (Asn)³⁴⁰ increased in the IgAN group compared with that in the ORD group (<i>P</i> = 0.0189) and decreased post-treatment only in the T-CST group (<i>P</i> = 0.0195).</p> Conclusion <p>The MS analysis of <i>O</i>- and <i>N</i>-glycoforms of IgA1 revealed substantial changes in their abundance in the T-CST group but not in the CST, CO, and ORD groups. Our study provides new insights into how specific treatments alter the IgA1 glycoform abundance.</p>