Human serum paraoxonase 1 (PON1) is physiologically associated with HDL and has been implicated in the prevention of LDL lipid peroxidation .The aim of this work is to study the association between PON1 activity and gene polymorphism and the presence of microvascular complications in type 1 diabetes mellitus. This study was conducted on 38 patients (13 complicated& 25 non-complicated) and 16 healthy control. Conclusion: PON1 Q192R genotype, low PON1 activity and poor diabetic control in type 1 diabetes were associated with nephropathy.