Undisturbed soil samples were taken from the surface layers of the soil of El-Serw experimental station, Domitta governorate. after the harvesting of wheat crop to  demonstrate the effect of potassium fertilization and gypsum application under different irrigations water types on soil moisture characteristics and pore size distribution. The main obtained results can be summarized as follow: Soil moisture contents as well as soil moisture constants, i.e. field capacity, available water and wilting point increased under the addition of gypsum more than under those of potassium fertilization . Total soil porosity as well as pore size distribution were affected mainly by the additions of gypsum. Positive and high significant correlations have been established between soil moisture contents at field capacity and wilting point and either clay or organic matter contents. Otherwise , the percentages of coarse and fine sand were negatively affected at field capacity after irrigation with drainage water , such correlations were negative and significant at 1 % and 5 % between soil moisture content at wilting point and either coarse sand or silt, respectively for soil irrigated by Nile water. Results showed that soil organic matter contents affected positively and high significantly total soil porosity, Correlation coefficients between total soil porosity and either coarse or fine sand were negative and significant. More over, the volumes of quickly and slowly drainable pores are positively and significantly correlated  with clay content under drainage water irrigation. Also there was a high positive and significant correlation between fine capillary pores and organic matter content . On the other hand, negative and significant correlations established found between either slowly drainable or fine capillary pores and silt content in soil irrigated with Nile water.