Natural radioactivity was estimated in building materials using γ-spectroscopic method. Samples of granite, bricks, concrete and ceramic were collected from different places in Egypt. Samples were prepared for physical and mechanical properties measurements as well as the radioactive content. Gamma spectrometer composed of NaI crystal connected to ORTEC analyzer was used for radioactive measurements. Standard sample was prepared with the same geometry factor in NIS using a standard source traceable to NIST. Data of 238U, 232Th and 40K activities were collected, where the effective dose was calculated by the aid of UNSCEAR. Diffusion equation was used to estimate the Radon animation rate from the building materials used in model rooms estimated. It was found that the average of 238U, 232Th and 40K in the studied materials were for granite 63.4, 2.42, 1010.91 Bq/kg, for bricks   20.12, 3.75, 27.25 Bq/kg and for concrete 34.23, 2.36, 506.357Bq/kg. In spite of using materials with permissible activity concentration, the radon emission in model rooms was beyond the safe limits for inhabitants. The maximum dose from Rn concentration was 1.23 mSv/y. This concentration was affected by the space dimension, passing time and the building material radioactivity as well as ventilation. The most powerful factor affecting the radon concentration is the ventilation.