This study aims to determine the clinical significance of positive antinuclear/antiextractable nuclear antigen (ANA/A-ENA) antibody on manifestation and therapeutic response of childhood immune thrombocytopenia (ITP). Overall, 1,330 patients aged between 1 and 15.6 years diagnosed with primary ITP were retrospectively analyzed, excluding those with secondary ITP. Bleeding manifestations were recorded. All patients underwent autoantibody testing and follow-up for 32 months on average (range: 23–54 months). Steroid response was also assessed. Response rates were compared between ANA/A-ENA-positive and ANA/A-ENA-negative patients. Of all the patients enrolled, 84 tested positive only for ANA, 102 tested positive for A-ENA, 54 tested positive for both ANA and A-ENA, and 1,090 tested negative for both. Patients who were ANA/A-ENA positive were more likely to be female and older than 10 years. Patients who were A-ENA positive were more likely to have either persistent or chronic disease and suffer from life-threatening bleeding as well as poor short-term therapeutic response. We conclude that autoantibody testing is important to determine the short-term prognosis of ITP patients. Females, patients older than 10 years of age, and patients with either mixed positivity or A-ENA positivity should be more closely monitored.