Authorities have discretionary power when practicing some of its administrative functions. However, in all cases, such power must be practiced within the limits and scope of the Principle of Legality in a broad sense, which acts as fundamental security to ensure that all State functions are subject to the Law, including the alignment of its decisions with the General Principles of Law. Under the General Principles of Law, the Proportionality Principle was established by the Administrative Jurisdiction to ensure Authorities' decisions are aligned with the enormity and seriousness of the causes by selecting the most appropriate, most necessary, and least restrictive actions. To achieve the Principle of Legality, the Administrative Judge, being the guardian of individuals' rights and freedoms should observe the Authorities' decisions and procedures and ensure they are commensurate with the seriousness of the causes and interests to be achieved. Additionally, the Principle of Proportionality is widely used around the world, given its significance. In fact, some States have stipulated it in their constitution and implemented under their administrative regulations, to preserve public order while restricting individual rights and freedoms. As such, the State is able to achieve a balance between protecting its general interest and the rights of the individual. The importance of this study revolves in dealing with modern trend of Administrative Judicial oversight related to apply the Principle of Proportionality to the decisions taken by Authorities, given the absence of previouse studies dealing with the Principle of Proportionality in the Sultanate of Oman, whether by analyzing the topic, rooting it, or comparing it with the comparative judiciary. So, results and recommendations of the study will arise practicl benefits for Authorities to know the limits of thier discretion in restricting the rights of individuals. As for the methodology used in the study, it has taken the analytical and comparative approach, which is based on analyzing the views of scholars, and defining the role of legislation and Omani judiciary, German and European Union judiciary in applying and devloping the Principle of Proportionality, due to the valuable status of Prnciple of Proportionality shown by both jurisdictions.