Type 1 diabetes mellitus (T1DM) is a chronic autoimmune illness defined by the gradual and selective destruction pancreatic beta-cells throughout childhood or adolescents. Anti-Glutamic acid decarboxylase 65 (anti-GAD65) is circulating autoantibodies to insulin secreting pancreatic β-cells antigens, and considered as one of the islet cell autoimmunity markers. Hemoglobin A1C (HbA1c) is a blood glucose monitoring measurement that is used as an indication of blood glucose average measurement over a period of several months. According to the significance of prior subjects and in order to have a greater understanding, this study is planned to evaluate the anti-GAD65 and HbA1c frequency and their association among T1DM children. One hundred of new onset T1DM patients consist of males and females with ages ranging from 1-15 years. Blood samples were collected for biochemical and immunological study. The present study results show anti-GAD65 in 87% were with mean concentration (69.03 IU/ml), 14% with mean concentration (3.8 IU/ml) of total T1DM patients. While the results of estimation of HbA1c level in the present study showed a total mean average of HbA1c was (11.22 %) in newly diagnosed T1DM patients. The association between anti-GAD65 and HbA1c showed that positive anti-GAD65 were with (11.75 %) mean level of HbA1c, in compared to (7.66 %) mean level of HbA1c in negative anti-GAD65 T1DM group and that HbA1c levels were significantly higher, according to statistical analysis in positive anti-GAD65 patients than in those who had negative anti-GAD65 at (P < 0.01), suggesting that autoimmunity was found to be involved in glycemic indices reflected by HbA1c levels particularly among very young children who had been developed type 1 diabetes.