Objectives: This study aimed to investigate the association between immunoglobulin G (IgG) N-glycosylation patterns and the clinical endotypes of patients with idiopathic inflammatory myopathies (IIM), potentially informing disease classification and therapeutic target identification. Methods: We recruited 168 IIM patients and 52 healthy controls, and performed IgG N-glycosylation profiling using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and employed GlycoQuant for intact glycopeptide analysis. Clinical data were extracted, and statistical analyses were conducted to correlate glycosylation profiles with clinical manifestations. Unsupervised clustering analysis was applied to identify novel IIM subgroups based on differential IgG N-glycosylation. Results: Our analysis revealed significant disparities in IgG N-glycosylation between IIM patients and controls, with 13 specific glycoforms exhibiting marked alterations. The level of fucosylated glycans was significantly higher in the IIM patients than healthy controls. Three distinct IIM endotypes were identified, each characterized by unique glycosylation signatures and clinical phenotypes. These endotypes were not congruent with conventional diagnostic subgroups and demonstrated associations with various clinical outcomes, including muscle weakness, interstitial lung disease (ILD), and serological profiles.