Salinity of soil and water resources is one of the most important problems which reduce agricultural productio and gradually decrease the area under cultivations. Salt accumulation in the soil profile is one the major problems in irrigated lands, in arid and semi-arid regions. Irrigation water even with the best quality, carries some soluble salts to the soil and increase the soil salinity in most of the cases. Considering the scarcity of water resources for agriculture, irrigation with poor quality waters is being increasing. One of the effective methods of reducing the salinity hazard is the application of leaching and leaching management. In this study the effect of three irrigation water qualities of 1, 3 and 5 dS/m and three leaching levels of 0, 20 and 40 percent on yield and yield components of soybean and some chemical characteristics of soil and drainage water in a loam texture soil was investigated.The soybean variety that was selected fot this study was Gorgan-3. The study was carried out in a greenhouse at the College of Agriculture, Isfahan University of Technology in completely randomized design as farctorial with four replications. The results showed that as the salinity of irrigation water increases and leaching level decreases, the soil salinity, sodium adsorption ratio and exchangeable sodium percent increase and these increases are greater for soil depth of 0-15 cm as compared to soil depth of 15-30 cm. The increase of irrigation water salinity and leaching level increase soil pH and soil pH was greater at the lower soil layer as compared to the top layer, but the differences were not significant. With increase of quality and quantity of leaching water, the soybean grain yield, plant elevation, flowering duration, riping duration, weight of 1000 grains, plant dry weight, number of filled pods, number of all pods, seasonal evapo-trairation and harvest index increase but number of infetile pods decrease. The study of Mass-Hoffman equation showed that the parameter of “a” is equal to 1.32 dS/m and the parameter of “b” is equal to 17.2 percent per dS/m increase in soil salinity. From comparison of the results of this study with the previous studies for soybean, it can be concluded that as soil salinity levels increase Gorgan-3 variety has less threshold decrement yield but has better tolerance to salinity. The study of Stewart equation showed that the parameter of “b” in this equation is equal to 2.77. As salinity of irrigation water increased the salinity of drainage water increased. Application of leaching in the best and worst applied irrigation water qualities (salinity of 1 and 5 dS/m) had the most and least leaching efficiency, respectively. The most saline drainage water and the most changes in salinities of drainage waters were belonged to the four first irrigations at the beginning of the season. In the later irrigations the changes in salinity of drainage water decreased significantly and the changes became nearly consonant.The changes in pH of drainage water were irregular and the changes were not significant and it increased during the irrigation season. The reason of these irregular changes were changes in concentrations of carbonate and bicarbonate ions in the drainage water, which these ions concentrations changes caused by the changes in temperature and air pressure of environment. Keywords: Salinity, Leaching, Soybean, Harvest index