Rey city had been important during the history of Iran significantly due to it's geographical location in the path of highway which related the east to the west and north to the south. The claimants of power in Iran always tried to dominate this city. By consolidating the power of Saultan Mahmoud Ghaznavi in the east, he planned an ambitious idea with a religious appearance to begin his expansions in western _central Iran, Arab Iraq and Egypt Fatemian domain and he occupied Rey at the first step. From then Rey became a expansionism command post for Ghaznavian. This paper aims to study the position of Rey in the expansionism policy of Mahmoud Ghaznavi, It's objectives and outcomes in a descriptive _analytical method. Findings show that with respect to the weakness and inability of Majd Al Dolle_a Boihi ruler of Rey_and his request for help from Sultan Mahmoud, the grounds were provided for Ghaznavian dominance on Rey. Sultan Mahmoud viewed Rey conquer as a source to reach the predetermined porpuses especially reaching Baghdad and overcoming Abbassi Caliph, , but by his death and discrepancies among his children, Ghaznavi conquers in central of Iran were stopped.