The study aims to explore nature of military organizations in Oman during 132 AH-280 AH/ 749 AD- 893 AD, starting with the factors of their rise and development, and highlights internal details of those organizations, and the related supplies and equipment. The study indicates military strategies and tactics that were adopted, and concludes the marital rules and ethics to which Omanis adhered in the battlefield. The researcher adopted in his study several interrelated methodologies, such as the historical methodology based on history and time tracking, in addition to inductive, analytical, and comparative methodology. Those methodologies depend on the juristic bibliographies and books of Omani biographies that were available to the researcher. In addition, the researcher referenced the books of history, geography, lineages and literature, and literatures that were beneficial to the researcher in some points related to the course of the study. The study was divided into introduction, three chapters and conclusion. Introduction handled definition of military in language and terminology, in addition to clarification of the Islam's end of establishing military systems. introduction ended by inferences from the military history of Oman in Rashidite and Umayyad eras. Chapter one addressed the external and internal factors that formed the military system in Oman, and tracked the roles assumed by the army of Oman in its land and sea divisions in aborting the internal riots and encountering the foreign attacks. It also indicated nature of human and material supplies of military organizations. Chapter two handled military strategies and tactics adopted by Omanis in their wars whether before or during the war. Chapter three clarified the marital rules and ethics that were applied by Omanis whether before, during or after the end of war. The study drew package of conclusions, including: That foreign invasion of Oman was driven by doctrinal, political and economic reasons. Reliance by Abadite Imam on irregular army didn't prevent imposition of security and stability. The study revealed the role of jurisprudence in determination of the features of military organization. The study concluded that national unity is the most powerful weapon in protection of the country and defeat of enemies.