The study aimed at investigating to what extent principles of Global citizenship are incorporated into social sciences textbooks for Grades (10-12) and its challenges from the point of view of the curriculum designers in Oman. The data was collected through using a mixed method. The researcher used analytical checklist that included (49) topics and (5) main citizenship principles, which are: international peace, human rights, human and environment, democracy, and multi cultures. A checklist of eight questions was implemented by the researcher. After the validity test, fourteen social sciences textbooks based on Ministry of Education (MOE) and thought at Islamic Institutes were analyzed for Grades (10-12)/ semester 2019-2020. Seven semi structured interviews were conducted with curriculum designers from MOE and Sultan Qaboos Higher Center for Culture and Sciences. The results of the study revealed that 2625 instances of incorporating principles of Global citizenship and its topics in the social sciences textbooks were offered by MOE and taught at Islamic Institutes for Grades (10-12). Results also showed that the most repeated principle was human and environment with 761 instances and 29 %, the democracy principle was the less repeated with 93 instances and 4%. Moreover, the study found out that several challenges were encountered by the curriculum designers in incorporating international citizenship principles: numerous amounts of knowledge and new global issues have appeared, and challenges related to educational policies and technical sides. Based on the results, a number of recommendations were proposed for further studies.