Hypothyroidism is one of the most common endocrine gland diseases. Also, it effects on all individual’s males, females, young, elderly, every races and levels of educations, urban residents and rural. As well as, it effects on all people with different socio- demographic characteristics. Poor knowledge of the patients with hypothyroidism concerned self-care can change in their lifestyle, deteriorate symptoms and complications. As a result the proposed instructional program for hypothyroidism patients’ knowledge regard self-care may improve in their lifestyle, decrease symptoms, adapt with illness and prevent complications. The main objective of the current study is to evaluate the effectiveness of an instructional program on hypothyroidism patients’ knowledge toward self-care. A pre- experimental design (one group before the test– after the test) was used to conduct this study at Baghdad teaching hospitals for period from 25th February, 2021 to 28th July, 2021. A non-probability (purposive) sampling was used to select (50) patients with hypothyroidism were attending to the endocrine clinics (out patients clinics) in Baghdad teaching hospitals. The validity of the questionnaire and the instructional program were verified by presenting it to (21) experts. The reliability was determined the knowledge questionnaire by using (test and retest) approach. Statistics were used to analyze the results of the study using Statistical Package of Social Sciences (SPSS) version (25). The study findings show that are a highly statistically significant differences between the scores of the patients’ knowledge in two levels of measurements (pre- test and post-test) at (p<0.01), where the statistical mean of the overall knowledge of patients in the pre-test was (p= 0.357), while it becomes (p= 0.870) in post-test. Furthermore, there is no relationship among age, gender and level of education variables and hypothyroidism patients’ knowledge toward self- care at (p>0.05) in pre and posttest. The study concludes that the instructional program positively effects on the hypothyroidism patients’ knowledge concerning self –care. The study recommends that applicate future studies on large populations and keep the instructional program continuous by providing frequent leaflets containing self-care guideline to each patient with hypothyroidism to improve their knowledge regarding self-care.