Oman is characterized by its arid climate. This is natural, in view of its location along the Tropic of Cancer, in a zone dominated by the subsident limbs of the Northern Hemisphere Hadley Cell circulation. However, the coastal position of Oman at the south-eastern end of the Arabian Peninsula, plus its high mountain range (Hajar Mountains) in the north both help to induce quite significant annual mean rainfall in a few favored areas. There are several factors that determine the overall impact of the climate change. Precipitation will be one of the most critical factors. Compared to air temperature, precipitation is difficult parameter to predict. For every degree centigrade, global scale researches showed that water vapor will increases by 7%. Based on these researches, it is less clear how this will that will impact the total change on precipitation. On the other hand, an increase of about 1–2% on the total volume of precipitation is likely to happen for each degree of warming. The main objective of this paper is to investigate the effect of climate change on the water resources and rainfall in Oman. It presents climate projection based on different Representative Concentration Pathways (RCPs) namely RCP2.6, RCP4.5, RCP6.0 and RCP8.5. The climate projection was based on Hadley Centre Global Environment Model version 2 (HadGEM2) downscaled to 1 km resolution. It was projected that slight dryness will take place over Hajar Mountains based on RCP 2.6 during 2041–2060. The effect of the dryness is projected to cover wider areas based on the other RCPs scenarios except Dhofar region. RCP 8.5 projected wetter climate over Dhofar region during the period of 2061–2080.