Background and Aims: Alpha 1 antitrypsin (AAT) is an inhibitor of serine protease, which has shown anti-inflammatory reactions in a variety of diseases. It has been thought that that AAT plays a role in prolonging islet allograft survival, preventing the development of type 1 diabetes mellitus (T1DM), and hindering β-cell apoptosis of pancreas. In the current examination, the AAT activity in T1DM and healthy individuals was measured using enzymatic assay. Methods: The present study was conducted on 42 patients with T1DM who referred to the Diabetes Clinic of Rafsanjan, Kerman, Iran, and 42 healthy control individuals who were matched for age, sex and smoking habits. The serum trypsin inhibitory capacity (TIC) was assessed. Plasma samples were analyzed for phenotype, AAT concentration, blood glucose and lipid levels were measured. Results: The activity of plasma AAT and the serum TIC level of patients with T1DM (2.35 ± 0.34 μmol/min/ml) was significantly lower than healthy participants (3.36 ± 0.36 μmol/min/ml). The frequency of phenotype MM in healthy individual was 100%; and in T1DM patients, the prevalence of phenotype MM, MS and MZ was 61.9%, 23.8% and 14.3%, respectively ( P < 0.001). Conclusions: It was concluded that that the lack of AAT may be related to the increased risk of T1DM developing.