Our present work was focused on the effect of grain size on the emanation coefficient, mass and area exhalation rate in different grain size of the soil, phosphate and building material samples. These samples were fractionated into seven-grain sizes each (2000-1800, 1800-1000, 1000-560, 560-425, 425-200, 200-80 and< 80 μm) and employing AlphaGUARD to determine the radon exhalation rate in these samples. The data analyses were performed to determine emanation coefficient, mass and area exhalation rate. Results revealed an inverse relationship between radon exhalation and grain size in soil and building materials (sand, granite and marble) samples while the trend is not clear in the phosphate and limestone samples. The emanation coefficient of Rn-222 was constant in different grain sizes of all samples.