Abstract: The microwave signal depolarization caused by storms particles is one of the major problems in utilizing microwave bands for terrestrial and space communication especially at desert and semi desert area. This aim of this research is to study the effects of dust particles on the polarization state of microwave signal. The calculations, which were based on the probability density of Iraqi dust storms, were performed for six frequency bands of microwave signals. Results showed that strong and severe dust storms can highly depolarized the microwave signal through induced differential attenuation and differential phase shift. These two parameters also depends on the shape of the dust particle, particles with low axial ratio can induce relatively high differential attenuation and differential phase shift, and therefore cause more depolarization in the signal. It was found that the relative humidity can only affect the differential attenuation and this effect is minimized at band of high frequency.