This study is summarized in defining the International Criminal Court (ICC) and the effects resultant from the joining of Sultanate of Oman to ICC. In the beginning I focused on ICC regarding historical background of establishment and the phases it went through and explain its unique features that make it different from other Judicial structures, especially it resembles a qualitative move in the international criminal judiciary being an independent criminal judiciary entity through which it pursuits international criminals within its specialty and guaranty that no criminal shall escape punishment. The study also comprised the motives behind joining ICC and views thereto, and at the same time examining the situations of some countries regarding such joining as we dedicated the position of Arabic Countries in this issue. As the main study theme was the effects resultant from joining the ICC, it included other than the previous chapter, two chapters pertaining to these effects one of them tackles the resultant effects related to internal dimension (national laws), and the other relates to international magnitude (the international law and the court). The second chapter that included resultant effects from the Sultanate joining the ICC with respect to the national law, concluded within its discussions tendency to detail every theme upon the resulting effects in one particular national law into a group of effects some of which are in legislative conformity with Rome Basic System of the ICC while others are not. Thus we were tended towards specifying aspect of variance and how to reach legislative conformity between Omani laws and the basic system of the ICC. This chapter worked for exploring these legislative conformities between the two systems regarding a group of pertinent national laws starting with the State's basic system, criminal laws and law of handing over criminals together with the Military Courts law. The third chapter reached the same conclusion with the second chapter as for explaining issues of conformity depending on considerations of joining the ICC albeit there is difference in determining effects because this chapter examined the international dimension as an extension to the internal scope covered in the second chapter to reflect exclusivity to all effects resulting from the Sultanate joining ICC whether regarding national or international laws. The third chapter in considering such effects included the effects resulting as for the international law and what relates to the ICC, while deducting legislative conformities for both issues should such effects require such conformity and find legal proposals and solutions to such conformity. Finally, the study reached a package of conclusions deducted from the three chapters, as also the researcher viewed necessity to present some recommendations and proposals where he sees adoption of such aspect is crucial to the Sultanate the most significant of which: Importance of applying to membership in ICC. - Issue of a special law or amend the Omani criminal law or punitive law to include all crimes that fall within specialty of the ICC. Formation of Arabic Association to deal with matters related to the system and activity of ICC not to mention the European Union in this regard.