Background and Aim: Increased oxidative damage due to overproduction of free radicals in diabetic patients has already been reported. Complications in lipid membrane, as a consequence of free radicals’ activities, have proved to be associated with an increase in serum malondialdehyde (MDA) a lipid peroxidation end-product marker. Therefore, this study was performed to assess the effect of controlling diabetes on lipid peroxidation in type II diabetic patients. Materials and Methods: This case-control study was conducted on 127 type II diabetic patients who were divided into two groups with respect to their serum HbA1C Level. Sixty four patients in the controlled group (6%≤HbA1C≤8%) and 63 cases in the uncontrolled group (8%< HbA1C) were studied. Serum biochemical parameters such as fasting blood sugar, triglyceride, cholesterol, HDL-C, LDL-C and variables such as age, duration of diabetes, cigarette smoking, body mass index (BMI), were determined in the two groups. The obtained data was statistically analysed by means of SPSS, independent t, and Chi-Square at the significant level P≤0.05. Results: Serum MDA level in the uncontrolled diabetic patients was significantly higher (P=0.025) compared to the controlled ones (2.01±0.88 and 1.63±1.01 nmol/mL, respectively). The levels of fasting blood sugar (208.6±61.6, 159.9±33.0 mg/dL) and triglyceride (223.9±131.8, 182.2±95.4 mg/dL) were significantly higher (P=0.001 and P=0.43, respectively). In the uncontrolled group, mean age of patients in the controlled group was significantly higher (P=0.036) than that of the uncontrolled group (57.73±9.25 and 54.38±8.59, respectively). Conclusion: The results indicate increased lipid peroxidation in the uncontrolled diabetic patients. Thus, controlling diabetes as a prophylactic procedure can reduce complications resulted from this increase in type II diabetic patients.