Abstarct: In nature, can be found soils that under the same stress, with increasing the percentage of moisture will reduce lot volume. This leads to collapse in the structure of soil and ultimately causing a large settlement in soil. Such soils that are found in dry and desert areas, are known collapsible soils. With relatively large expansion of collapsible soils in Iran and need for the development of cities, the need to evaluate the potential of soil’s collapse becomes more and more evident. In this study, we examine the effects of environmental pollutants that are acidic or basic on the behavior of collapsible soils. The aim of this study was to evaluate the potential of collapse due to saturation of the soil caused by the infiltration of contaminants such as leachate and waste water and chemicals into the soil. For this reason, natural leachate produced by the Mashhad landfill was used in experiments and testing was performed collapse in saturated conditions with natural leachate and was compared with terms saturated with water. Also Since the possibility of separation of leachate components, especially in the life of different ingredients and different pH did not exist, so the two factors sulfuric acid and sodium hydroxide as representatives of the leachate and the pH of 1 to 14 were used and collapse tests on soil samples and in conditions saturated with leachate was performed. Also The effect of percent of pollution on soil collapse were studied, so that the weight percentage of soil samples with 5, 10 and 15 percent of natural and synthetic leachate was infected and infected samples were tested on collapse. the results show that natural leachate creates more collapse rather than water in soil. Also in relation to the effect of pH on the rate of collapse, results show that leachate with low pH and acidic increases the potential of collapse of soils and Leachate with high pH and alkalinity, make up less collapse. Also range of soil’s collapse in low pH and acidic is much more than high pH and alkalinity. In other words, Changes in soil’s collapse caused by one or two unit change in pH toward acidic is much more than the same change to alkaline side. In relation to the impact of percent of pollution on the collapse, results show that by increasing the percentage of natural leachate were increased amount of soil collapse. Also, with increase of percent of synthetic acidic leachate in soil, were increased the amount of collapse, but with increase the percentage of synthetic leachate in an alkaline state in the collapse not seen much difference, because this experiment, was performed in state of saturate with water, that has caused, the final pH of the soil, does not change much and collapse remain stable.