Abstract： Objective To establish a radioligand assay for SOX13 antibody (SOX13-Ab),and to explore its diagnostic role in autoimmune diabetes. Methods ~ 35 S labelled recombinant human SOX13 antigen was obtained by in vitro transcription and translation, and then was mixed with serum samples in rotating incubator overnight. The immune complexes were precipitated with protein A-sepharose, then washed with TBST buffer. The radioactivity was counted on a liquid scintillation counter. The results were expressed by international standardized antibody index. Sera from 162 diabetic patients with acute-onset, 328 patients with slow-onset and 120 healthy controls were tested for SOX13-Ab. Results The intra-assay coefficient of variation(CV) was 3.9%～9.2%, inter-assay CV 5.2%～12.0%. The upper limit of the normal range was defined as the 97.5 percentile of the SOX13-Ab indexes measured in the sera of 120 healthy controls. The cut-off value thus obtained was 0.1. The prevalence of SOX13-Ab was 2.5% (3/120) in healthy controls, 9.3% (15/162) in acute-onset diabetes and 10.4% (34/328) in slow-onset diabetes. The frequencies of positivity for SOX13-Ab were higher in acute-onset, slow-onset diabetic patients than that in healthy controls (P<0.05). Conclusions The established SOX13-Ab radioligand assay has a high sensitivity and reproducibility, which can be used in clinical practice. The higher frequencies of positivity in acute-onset and slow-onset diabetic patients suggest the unique diagnostic role of SOX13 antibody in autoimmune diabetes.