Objective To investigate the correlation between granulocyte-macrophage colony-stimulating factor (GM-CSF) antibody levels and disease severity in autoimmune pulmonary alveolar proteinosis (PAP). Methods A retrospective analysis was conducted on 18 patients with autoimmune PAP. Serum GM-CSF antibody levels were measured, and pulmonary function [diffusion capacity of the lung for carbon monoxide as a percentage of predicted value (DLCO%pred) and forced vital capacity as a percentage of predicted value(FVC%pred)], oxygenation index, high-resolution CT imaging scores (percentage of ground-glass opacification/consolidation in each lobe and proportion of Hounsfield unit partitions) were evaluated. Spearman correlation analysis and comparison between high- and low-antibody groups were performed. Results A total of 18 patients were enrolled, with GM-CSF antibody levels ranging from 66.2 to 445 U/mL. Correlation analysis showed that GM-CSF antibody levels were not significantly correlated with DLCO%pred, FVC%pred, oxygenation index, disease severity score, or the percentage of whole-lung ground-glass opacification/consolidation. No statistically significant differences were observed in any severity indicators between the high-antibody group (>400 U/mL) and the moderate-to-low antibody group (≤400 U/mL) (P>0.05). Conclusions Although GM-CSF antibody level is a key diagnostic marker for autoimmune PAP, it cannot serve as a reliable biomarker for assessing disease severity. In clinical practice, judging disease severity based on antibody titer should be avoided.