The present study deals with investigating radon level in groundwater, which is being used for irrigation in the environs of Qassim province, Saudi Arabia. Ninety nine samples of groundwater were collected from eight cities in Qassim province. Radon concentrations in the collected water samples were measured with RAD7 electronic radon detector connected to RAD- H2O accessory (Durridge Co., USA). The concentration of (222)Rn in 99 irrigation groundwater samples ranged from 1.20 to 15.43 Bq l-1Radon level in? 5 samples 2 from Al-Asyah, 2 from Al shamasia and one sample from Al Moznib exceeded the permissible level of radon 11 Bq l-1 in groundwater. The total annual effective dose varied with increase in radon concentration. The calculated effective dose per liter (EDL) and annual effective dose (AED) ranged from 6.1 to 77.15 nSvL-1 and 4.45 to 56.16 μSv y-1, respectively. It was evident that the total annual effective doses resulting from radon in 95% from groundwater in Qassim area were significantly lower than the permissible limit of 1 mSv y-1 for the public.