Objectives: Type 2 diabetes mellitus (T2DM) is emerging as one of the world's greatest health problems, and its incidence and prevalence are increasing at an alarming rate and globally reaching epidemic proportions. With this increasing incidence, emphasis is now being placed on implementing primary prevention, early detection, and educational prevention programmes. This study was undertaken to estimate the level of knowledge of T2DM among high school students and to explore the factors influencing the knowledge of T2DM. Methods: A cross-sectional study was conducted in four secondary schools in two wilayats (districts) of Muscat governate, Oman, namely Al-Amerat and Quriyat. The study was conducted using a validated English questionnaire covering all aspects of T2DM in one-to-one interviews. A scoring system was used to assess the students' knowledge. Results: Of the 541 students enrolled in the study (45% male and 55% female), only 24% achieved a score of over 10 out of 20. The key areas of poor knowledge were wrong perceptions about diabetic meals (73%), and the possibility of a cure for diabetes (63%). Conclusion: Overall poor knowledge levels about T2DM were found among school students. National efforts and school health-based interventions are highly recommended to increase awareness about diabetes among this age group.