Rn-222 is the most important source of natural radiation and is responsible for approximately half of the received dose from all sources. Most of this dose is from inhalation of the Rn-222 progeny, especially in closed ares. Portable alpha particle detector, RAD7 was used for Rn-222 measurements inside the main campus of Aljouf University at Saudi Arabia in order to estimate the effective dose to the occupants from ²²²Rn and its progeny. The values of annual effective doses for radon inhalation by the inhabitants were found to vary in the range 0.08 - 0.80 mSv/y, with a mean of 0.4 mSv/y. These results are lower than the value 1 mSv/y recommended by ICRP, 1990. The variation of dose relationship from indoor radon in lung tissue is calculated and tabulated. In addition to environmental value of the present survey, the results are considered to be essential in analyzing any data for future activities in this field.