Background: Type II diabetes mellitus (T2DM) is a chronic condition that needs complete self-management, which is severely guided by a patient's understanding of the disease, their everyday health behaviors, and their total well-being. Aim: to assess knowledge and quality of life among adults with type II diabetes mellitus. Design: A descriptive correlational research design was utilized in this study. Setting: The study was conducted at Al Bandar Primary Health Care Center, Yanboa Ebahr, KSA. Sample: A purposive sample 124 patients with diabetes type II attended chronic diseases clinic. Tools: Data was collected using three tools. 1st: demographic and medical data questionnaire, 2nd: adult knowledge questionnaire regarding diabetes, and 3rd: MDQoL-17 questionnaire for adults regarding diabetes type II. Results: The results revealed that (44.5%) had satisfactory level of total knowledge scores and (55.6%) had a better quality of life. Conclusion: there were a highly statistically significant differences between males and females' patients with diabetes type II regarding their knowledge and quality of life where mean knowledge for female patients was higher than males while mean quality of life of males' patients were higher than females. Recommendations: The health care organizations should develop structured, culturally tailored diabetes education programs.