Rational, aims and objectives: This study aimed to assess knowledge, attitude and practice (KAP) of using insulin pen in diabetes and determine the related factors to the KAP, adverse drug reactions (ADRs) and glycemic control status. Methods: In our descriptive study, 148 patients with diabetes were interviewed by 16-item questions on knowledge and 8 questions on attitude, and were asked to present the insulin pen injection technique with a sample insulin pen. Results: Proportions of patient having a good knowledge, positive attitude, and good practice were 45.9%, 78.4%, and 44.6%, respectively. The three most incorrect steps were skipping to prime pen needle (90.9%), not removing the used needle from the pen after using (87.8), and not holding for specific count time before withdrawal of pen needle from skin (50.7%). Patients having duration of insulin one year or more had better knowledge (p=0.025), more positive attitude (p=0.017), and better practice of insulin (p=0.042). Patients using insulin combined with oral diabetic medications or having history of using insulin vials had more positive attitude of insulin role (0.038). Frequency of having good knowledge was statistically significantly higher in participants who received counseling from health professionals previously (p=0.001). The study also found a positive correlation between good knowledge of patients and good practical skills (p<0.001). Patients with poor practice of insulin were more likely to have ADRs at the injection sites (p = 0.013). The worse knowledge of patients was significant related to the higher risk of hypoglycemia (p=0.001). KAP levels did not correlate with glycemic control status. Conclusions: Positive attitude in patients was recorded at a significant rate; however, knowledge and practice needs improvement. This study was helpful to shape the patient education and target specific patients for education.