Administration requires discretionary power to ensure that the flow of public services is regular and constant. Through this power, administrative actions are managed in conformity with the sequential development in the field. Although Discretionary power is practical necessity with bright sides, it has a dark side when it turns into an absolute power that threatens the legitimacy and integrity of law, as well as the rights and freedoms of individuals. Hence, there has been a great need for a judicial control to eliminate this power and bring it to reason when deviating from the right path. As a result, in addition to traditional controls, the theory of manifest error in discretion and the theory of balance between benefits and damages have occurred to control discretionary power. According to the methodology of this research, the study is divided into an introductory preface and two chapters. The preface introduces the definition of discretionary power and the traditional controls over it, while the first chapter sheds light on the theory of manifest error in discretion, as it explains the definition of the theory, its origin, criteria and judicial applications. The second chapter concentrates on the theory of balance between benefits and damages, and clarifies its definition, origin, criteria, controls and judicial applications in the Sultanate of Oman and comparative judiciary. The research concludes with the results and recommendations of the researcher that contribute to the administrative judiciary and legislative power in Oman, and aim to throw light at the necessity of controlling discretionary power.