In recent years, amending soil with biochar is considered for the purposes of sequestering carbon, improving soil fertility, and immobilizing environmental pollutants. Application of acidic biochar is a promising approach to improving physical, chemical, and biological properties of the alkaline soils in arid and semi-arid regions. The present study aimed to investigate the effect of some acidic biochars as a conditioner for a calcareous soil of Isfahan Province (Central Iran). The biochars of rice husk (RH) (pH=5.64) and pine cone (PC) (pH=6.56) pyrolyzed at 300°C. Treatmentsof the study were included the two types of biochar, at one, three and six percent of biochar, two sandy loam (Tiran) and clay loam (Lavark) soil textures, and two incubation periods of one and six months, and 4 controls with a total of 28 treatments. The treated soils were incubated at 25°C and 60% of field (pot) capacity moisture content. At the end of the periods (three and six months), the effects of biochars on soil properties were obtained. The study was conducted in a completely randomized and factorial design with three replications. The results showed that the application of biochar in all treatments caused a decrease in soil pH values compared to the control. Amendment of the clay loam soil with 6% of RH biochar caused a significant reduction of 0.35 units compared to that of the control after six months of incubation. The use of biochar also caused a significant increase in the soil electrical conductivity in most treatments, and the maximum increase (0.19 dS m - 1 ) was recorded for the sandy loam and 6% PC biochar. After 6 months of incubation, using biochars caused a significant increase in soil organic matter contents in all treatments except for the sandy loam soil and 1% ??PC. The application of 6% biochar also caused a significant increase in the total nitrogen of the soils compared to the control. The addition of 6% PC biochar to the sandy loam soil had the highest significant effect on increasing total nitrogen content compared to the control. With increasing the amount of added biochar from 1% to 6%, a significant increase was observed in the amount of available phosphorus in sandy loam soils and a significant decrease in the clay loam soils. Even after one month of incubation, treating of the sandy loam soil with RH biochar increased available phosphorus by 23 mg kg - 1 compared to the control,. The highest increments in the soil available potassium and iron contents (270 and 4.5 mg kg - 1 , respectively) were observed in the clay loam soil treated with 6% PC biochar, after six months of incubation. The highest increases in the amounts of soil available zinc were 3 and 1.5 mg kg - 1 compared to the control observed in the clay loam soil after one month of incubation with 1% PC and RH biochars, respectively. Treatment of sandy loam soil with 1% RH biochar also increased the amount of available copper in the soil by more than 0.25 mg kg - 1 compared to the control after six months of incubation. The addition of biochars to the soils significantly increased the available manganese in all treatments. Applying 6% biochar into all treatments increased the frequency of medium soil pores. Application of PC and RH biochars at the rates of 3% and 6% caused a significant increase in available water (AW) in sandy loam soils compared to the control. The application of 6% biochar in sandy loam soil and 3% and 6% in clay loam soil also caused a significant increase in the physical quality index proposed by Dexter (S Dexter, fitting the Vannkhten-Moalem model), compared to the control. In conclusion, the use of acidic biochar, as an economically viable amendment, is recommended to increase the quality of soils in arid and semi-arid regions. Key Words Acid biochar, Biochar, Physical properties of soil, Soil remediation, Agricultural wastes, Special storage soils and natural resources, Rice paddy, Pine cone