Background and objective: Immune thrombocytopenia (ITP) is an autoimmune-mediated hemorrhagic disease, which is characterized by thrombocytopenia and bleeding manifestation. The treatment options of ITP in children are selected based on bleeding severities and the treatment selection is critical in children with a serious decline in platelet count (platelet count of <10×10 ⁹/L). Although it is well known that platelet-specific antibodies play a key role in ITP, the relationship between different platelet-specific antibodies and bleeding severities is unclear. This study aimed to analyze the relationship between platelet-specific antibodies (anti-GPIIb/IIIa and anti-GPIb/IX antibodies) and bleeding severities in children with newly diagnosed ITP and a serious decline in platelet count. Method: This study was a single-center prospective observational study that analyzed children with newly diagnosed ITP and platelet count of less than 10×10 ⁹/L from June 2018 to September 2021 in our Hospital. They were classified into mild-moderate and severe groups based on the treatments. Platelet-specific antibodies and titers were detected using a kit, PAKAUTO. We analyzed the relationship of bleeding severities with platelet-specific antibodies/titers . Results: A total of 86 cases were enrolled including 57 males and 29 females with a median age of 35 months (range 1 month to 198 months). And 11 cases were categorized as the mild-moderate group and 75 cases were categorized as the severe group based on bleeding severity score. The positive rates were 68.6% for anti-GPIIb/IIIa and 65.1% for anti-GPIb/IX. There was no significant difference in anti-GPIIb/IIIa and anti-GPIb/IX antibodies between the two bleeding severity groups ( χ²=0.530, P=0.467; χ²<0.001, P=1.000), and also no difference was found between the two groups when two antibodies were analyzed together ( χ²=2.071, P=0.558). The antibody titers in plasma and eluent were also detected, but no significant difference was found in the antibody titer ratios between the two bleeding severity groups ( P<0.05 in four plasma and eluent groups). Conclusion: Platelet-specific antibodies (anti-GPIIb/IIIa and anti-GPIb/IX antibodies) were not related to the bleeding severities in children with newly diagnosed ITP and serious decline of platelet count.