Background: Diabetes is a lifelong condition characterized by extreme blood glucose (or blood sugar) levels, which can cause major damage and complications to the heart, blood vessels, eyes, kidneys, and nerves over time. Objectives: Investigation of the effectiveness of patient’s instructional program using an assessment of patient’s knowledge, through the utilization of a knowledge test. Methods: The study carried out at Azady teaching hospital in Duhok Governorate. A quasi-experimental design (pre-post-test) study had been adopted through the present study with the application of the pre- post-test approach for both studied and controlled groups during the period 30 of March 2021 to 20 January 2022. In order to get reliable data and a representative sample, a nonprobability (purposive) sample was selected. The sample included in the present study is (54) patients. The sample is divided into two groups; (27) patients as the study group is exposed to the instructional program and (27) patients are not exposed to the program, considered as the control group. It is a questionnaire format for the research purpose and is composed of three parts. The first part delves into the social and demographic aspects of patients consisting of (14) items, which include (Age, gender, marital status, educational level, family income, diabetes duration, diabetes type), while the second part related to patients knowledge about diabetes and its complication, which consists of (7) items as multiple-choice questions. The third part consists of (12) items related to patients’ knowledge regarding management and control of their diabetes. Results: After applying for the instructional program, results were reported highly significant differences toward the effect of the program's contents through raising knowledge grades of studied respondents toward controlling their diabetes and preventing diabetes complications particularly at the post1 period. Recommendation: Instruction programs should be designed for all diabetic patients with both types of diabetes to improve their knowledge about the management of their diabetes and its complications and their knowledge should be updated periodically.