This thesis addresses an important legal matter which confronts most of the civil service officials, and in particular the legal researchers in the legal departments and divisions of the government units. This issue is the administrative investigation and its administrative and judicial guarantees in the Omani Law. We have used the analytic method in most cases for preparing this Thesis. We have also used the descriptive method in other cases. The Thesis is divided into two chapters, preceded by a preliminary one in which we have clarified the concept of the public officer, who is the focal point of the administrative investigation, as well as the concept of administrative contravention which is the reason for conducting this investigation. As for the first chapter, it has been dedicated to the authorities charged with conducting the investigation and their procedures. In chapter two we have reviewed forms of legal guarantees provided in favor of the public officer. In conclusion, we have reached a number of recommendations, the most outstanding among others are as follows: 1. It is necessary to set specific definition for the administrative contravention which determines the administrative responsibility of the public officer, in accordance with the stable constitutional principle in the Penal Code that says "No crime or penalty without a provision". 2. Adoption of the semi-judicial administrative interpellation system by adding members of the judiciary to the Administrative Interpellation Council and the Central Interpellation Council. 3. Preparation of an explanatory note concerning the administrative interpellation of public officers which will be a guide for the legal investigators in the administrative units of the government, so that their procedures shall be appropriate and in conformity with the provisions of the Civil Service Law and its executive regulations. On Allah We Rely To Sucreas"