This study reflects the important political and military events which happened in Mombasa, beginning from the Imam Saif bin Sultan Al Yarubi till the end of reign of Al Yaaribah dynasty (1696 – 1749 ). This period is considered to be one of the important periods in Omani history, especially the Omani – Portuguese conflict in East Africa in general and in Mombasa in particular , During this period the Omani forces seiged fort Jesus for almost three years which ended in the expuesion of the Portuguese from Mombasa to be chased to Mozambique. This was the beginning of the Omani rule of East Africa .Waeis terretayies were appointed in Mombassa to run the affairs of the African. As the Yaariba dynasty became weak the Mazruis claimed anindependent rule in the waliyat of Mombasa. This led to the start of a new conflict between the Mazruis and Al- Busaidi dynasty. Mombasa suffered from this conflict in a chain of conflicts between the Omanis with East Africans at one time and with the Portuguese at the other. This study consists of an introduction preface and three chapters. The introduction includes the objectives of fluriting this study, while the preface gives a general description of Mombassa, its topography and a historical background of the Portuguese occupation of East Africa and the Yarubi resistance till the reign of Imam Saif bin Sultan. The first chapter discusses about the siege of Fort Jesus and expulsion of the Portuguese from the coast and chasing them as far as Mozambique. The second chapter tackles how Mombasa was administrated by the Walis, the cirumstances and the political aims that made the Mazruis claim themselves, an inclcpendent rulers of Mombassa, the Al – Busaidi stand against his decision and its results. The third chapter is about the role of the Omanis in the development of social, economic and religious aspects in East Africa during that period of time.