Abstract: Background: Diabetes mellitus (DM) is associated with damage to target organs and premature aging and telomeres serve as a mitotic clock and biological marker of senescence. Aim of study: was to A) evaluate telomerase activity in both type 1 and type 2 diabetic patients with microangiopathy and macroangiopathy, B) to study the possible factors that affect the activity of this enzyme in these patients. Subjects and Methods: Study was carried out on 40 patients from those attending diabetes clinics of Banha University Hospital, they were divided into three groups: Group I: 10 type 1 diabetic patients with angiopathy (4males & 6 females). Group II: 10 type 2 diabetic patients with angiopathy (3males & 7females). Group III: 20 apparently healthy age & sex matched volunteers serving as a control group. The following laboratory investigations were performed to all patients: Plasma glucose (fasting and post prandial), Glycated hemoglobin, Lipogram (Total cholesterol, LDLc, HDLc and Triglycerides), Serum creatinine, Urinary microalbumin and Study of telomerase activity in whole blood. Results: Our results showed: that (HBA1C, microalbumin, creatinine, LDL, TG, TCH, PPBS and FBS)are significantly higher in diabetic patients compared to control group where (telomeraseand HDL) are significantly lower in diabetic patients compared to control group. Also, Telomerase activity was significantly low in diabetic patients with HbA1C (≥7%), LDL-c (>100mg/dl), HDL-c (150mg/dl), TCH (>200mg/dl), microalbuminuria (>30mg/ml) respectively compared to diabetic patients with HbA1C (