Deep soil-cement mixing is one of the popular methods in the field of soil improvement, including in sticky soils. According to available statistics, the use of this method in coastal areas has been more than other places. Coastal areas are adjacent to a large, accessible and free source of seawater, and if the adverse effects of seawater on cement are minor, its use will increase implementation speed, significantly reduce implementation costs and environmental hazards. However, according to the standards, the type of water used in all cement compounds is fresh water, and if seawater is used, its negative effects must be clear. The adverse effect of seawater salts on cement can be effective in reducing compressive strength. Based on this, the study on the decrease in compressive strength of soil and cement mixtures due to the presence of salts dissolved in seawater, will be useful in the design and method of deep mixing. In this study, by making samples of fine-grained clay soil, cement and seawater and comparing their unlimited compressive strength with similar samples prepared with fresh water, this has been investigated. The research was conducted in two general phases. During the first phase, soil-cement samples were made using seawater and cement percentages of 4 to 20% and water to cement content of 0.4, 0.5 and 0.6, which after processing in intervals of 7, at 14 and 28 days, they were broken. During this step, the optimal percentage of cement consumption was obtained. During the second phase, using the results of the first phase, two groups of soil-cement samples, using seawater and drinking water, with optimal water to cement percentages and cement percentages of 10, 6 and 14 were prepared and at processing times 7 days were broken for up to 240 days. The study of the growth rate of compressive strength of the mentioned samples with respect to time indicates that the unconfined compressive strength of the samples increases with increasing cement as well as