Background: The technique of monitoring patient’s blood glucose using a glucose meter is most useful as an adjunct therapy with pharmacological treatments against diabetes mellitus. The value and effectiveness of selfmonitoring of blood glucose (SMBG) is affected by the patient’s SMBG knowledge and skill. This paper aimed to quantify the impact of washing hands on accuracy result of capillary blood glucose measurements among diabetic patients. Patients and method: Quasi-experimental research design was conducted to meet the study's objective. In the internal medicine department at Assiut university hospital, Egypt. Sixty adult patients were eligible according to the inclusion criteria were enrolled. An interview questionnaire involved patients' demographic characteristics, clinical data, and knowledge regarding self-monitoring of blood glucose. Results: the mean blood glucose readings before washing hands were74.37± 86.594 mg / dl, 225.66± 85.973 mg / dl respectively after washing hands, and after peeling an orange followed by no washing hands were 349.03±90.084 mg / dl. Conclusion: The results of this study indicated that there was a statistically significant difference between washing hands and accuracy results of capillary blood glucose measurements. Recommendations: All patients should be advised to wash their hands with water and soap before performing the test.