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 ofBanha University Hospital, they were divided into three groups:Group I: 10 type 1 diabetic patients with angiopathy(4males & 6females),.Group II: 10 type 2 diabetic patients with angiopathy(3males & 7females),.Group III: 20 apparently healthy age & sex matchedvolunteers serving as a control group. The following laboratory investigations were performed toall 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 (<45mg/dl), TG (>150mg/dl), TCH (>200mg/dl), microalbuminuria (>30mg/ml) respctivelycompared to diabetic patients with HbA1C (<7%) , LDL-c (<100mg/dl), HDL-c (>45mg/dl),TG (<150mg/dl), TCH (<200mg/dl), and normoalbuminuria (<30mg/ml). There was significant relation between telomerase activity andmacroangiopathiccomplications, There was nonsignificant correlation between telomerase activity and each of creatinine level and age in the case group. Statistical analysis showed that 80% of diabetic patients (16 patients) were telomerase negative (lower than cut off value ≤49.20), whereas 20% of diabetic patients (4 patients) were telomerase positive (higher than cut off value > 49.20). Conclusion: it was concludedthat telomerase enzyme activity decreased in both type 1 and type 2 diabetic patients with angiopathy, There was a relation between telomerase activity and both micro &macroangiopathic complications.