Soil salinity and sodicity are important aspects of land degradation, especially in arid and semi-arid regions, where suffer from high values of electrical conductivity (ECe 4dS/m), exchangeable sodium percentage (Egt;15), sodium adsorption ratio (SAR 13) and low fertility. Gypsum is the most common chemical amendment that is widely used as a source of calcium for the reclamation of sodic or saline-sodic soils. Also, the addition of sulfur or sulfur-containing compounds is also one of the traditional methods for the reclamation saline-sodic soils. Sulfur is known to enhance plant growth in dry and alkaline soils through oxidation by soil microorganisms, which convert sulfur to sulfuric acid, which in turn reduces pH and improves soil structure. Therefore, in the present study, two chemical amendments of gypsum and elemental sulfur were used to improve these soils. As there is little information about the effect of chemical amendments such as gypsum and sulfur on the biological properties of saline-sodic soils, therefore, the present study investigates the effect of sulfur-containing amendments on the biological properties of these soils (first experiment) as well as the effect of Thiobacillus inoculation on the sulfur oxidation process time in soils treated with elemental sulfur. For this purpose, soil samples with different degrees of salinity and sodicity were collected from two regions of Roudasht (L 1 , L 2 , L 3 ) and Asgharabad (L 4 ) located in Isfahan province. Then, they were incubated with two amendment materials of gypsum and sulfur at levels of zero (control), 2.5, 5 and 7.5 Mg S ? ha -1 for 40 days. Some important biological properties such as basal microbial respiration, arginine ammonification, net nitrogen mineralization and immobilization, microbial biomass, activity of enzymes alkaline and acid phosphatase, and metabolic quotient were measured and calculated. Also, L 2 soil was used to investigate the effect of Thiobacillus inoculation on the sulfur oxidation process time at three levels of zero (control), 7.5 and 15 Mg S ? ha -1 of elemental sulfur amendment during 15 days incubation. The results showed that gypsum increased the amount of net nitrogen mineralization, urease enzyme activity and decreased metabolic quotient, and the sulfur amendment increased the processes of basal respiration, net nitrogen immobilization, acid phosphatase activity and metabolic quotient. However the type of amendments did not have significant effect on arginine ammonification, microbial biomass and alkaline phosphatase activity. Among the biological indicators considered, net nitrogen mineralization, acid phosphatase and metabolic quotient showed a higher response to the increase in the levels of amendment materials. The metabolic quotient showed a significant negative correlation with all the measured processes except for the basal microbial respiration. Also, the results showed that by inoculation of the Thiobacillus bacterium, even at the application level of 15 Mg S ? ha -1 , only by one day of incubation, thiosulfate, tetrathionate concentration and total of them reaches the zero (control) level, and This trend was observed in the absence of inoculation of Thiobacillus in the highest level of elemental sulfur application after 15 days. Keywords : Saline-Sodic soils, Gypsum, Elemental sulfur, Biological properties of soil, Thiobacillus bacterium, Sulfur oxidation, Total thiosulfate-Tetrathionate.