Background: Sleep disturbances are a common problem among patients with diabetes mellitus . Aim of the study: Assess sleep quality among elderly patients with diabetes Subjects and Methods: Research design: A descriptive design used to accomplish this study, Setting: The study was conducted at outpatient clinic and diabetic unit At Al-Ahrar Educational Hospital at Zagazig City in Sharkia Governorate. Subjects: A purposive sample of 200 diabetic patients. Tools of data collection: Two tools were used for data collection. Tool (I): a structured interview questionnaire included demographic data, medical history, knowledge scale for data collection. Tool (II): The Pittsburgh Sleep Quality Index (PSQI). Results: 86.5 % of the studied elderly patients were having unsatisfactory knowledge. On the other hand, 13.5% of them were having satisfactory knowledge regarding DM. Also, reveals that the mean score of sleep medication domain was the lowest between all PSQI domains .42 ± .65 while the mean score of sleep efficiency domain was the highest 3.00 ± .00. Conclusion: majority of the diabetic elderly had unsatisfactory level of knowledge about diabetes especially among those who illiterate, farmer, and having insufficient income. Additionally, most of the studied elderly had poor sleep quality and those elderly who were having chronic diseases especially more than two diseases reported poor sleep quality. Recommendation: Development of comprehensive simple Arabic printed educational materials such as pamphlets, books for increasing knowledge of the elderly patients about diabetes. Designing awareness programs and counseling sessions for diabetic elderly aimed at updating their knowledge and guiding them to better control of diabetes mellitus.