This study aims at studying the political relations between Najd and Hijaz districts between 1319AH/1902 and 1344AH/1926, as it is a very important period for the Arabian Peninsula. It is about deep rooted relations which go back into the 14" Hijri century/19th century such as those between Saudi Kings and the Nobility of Hijaz after the inception of the First Saudi Monarchy, and all the accompanying developments and results in later stages. And such as the relations between Prince Abdulaziz Al-Saud, governor of Najd and the Sherif Husain, governor of Hijaz who were trying to spread their authority over their lands. Many factors have played part in fuelling the disputes between them such as: 1. The role of tribal authorities which the kings and Nobles tried to pull to their side using different means. 2. The British policies and conflicting covenants with the political authorities in the Arabian Peninsula that aimed to support its interest and ambitions of expansion. 3. The failure of British authorities to conciliate the disputes between authorities, especially between Prince Abdulaziz and Sherif Husain which caused further disputes over borders. 4. The global developments preceding, before, during and after the First World War. The researcher will cite the preliminary sources regarding that period. The study is divided into an introduction, a preface, four chapters and a conclusion. The preface takes a brief look at the political status in Najd and Hijaz during the period since Mohammed Bin Abdul-Wahhab's missionary works and the inception of the first Saudi monarchy and till the end of the second Saudi monarchy; The first chapter takes the inception of the 3rd Saudi monarchy in 1319AH/1902 led by prince Abdulaziz and the joining of Najd areas and the Al Hsa in 1331H/1913. The second chapter is about the rise of Hijaz Kingdom led by Sherif Husain bin Ali in 1326AH/1908. The third chapter, focusing into the history of Najdi- Hijazi relations, starting from the point Sherif Hussain became the ruler of Hijaz and starting relations with Prince Abdulaziz through invading Najd. Meanwhile,. This chapter further looks at the developments accompanying the First World War such as Sherif Husain's declaration of rebellion against the Ottoman empire, while highlighting the British role on the relations between Hijaz and Najd before, during and after the War. The fourth chapter focused on the Kuwait Conference held to discuss the border issues between Iraq, Jordan and Hijaz, and how it failed leading to the Riyadh conference arranged by Prince Abdulaziz. It also discusses how this last conference gave the green light for the Najd troops to move towards Hijaz and take it through a series of dramatic developments forced Sherif Husain to step away from the rule, to became under the rule of Abdulaziz bin Abdulrahman Al-Saud.