Rangeland soils are ecologically very important. They cover about half of the world’s land. The presence of Zagros Mountains in Chaharmahal and Bakhtiari Province has resulted in a diversity of rangelands which play a vital role due to their special characteristics, geographical location, climatic conditions and geological formations. Parent material and topography are among the inherent soil quality factors. There is no detailed information, particularly in Iran , on the impact of such factors on soil quality. The objective of this study was to assess the effects of parent material and slope aspect on the surface soil and organic carbon quality. Three experimental range sites with different parent materials including dolomitic limestone, marl and conglomerate were selected 39 km south of Boroujen very close to each other. In each site, 20 surface soil samples (0-10 cm) were taken from each of the south and north facing slopes. Total organic C, pH, carbonates, KMnO 4 -oxidizable C at 60 (LC60) and 2 (LC2) minutes, microbial respiration (MR), ?-glucosidase activity, water-dispersible clay (WDC), cold water-soluble (CHcw), hot water-soluble (CHhw) and dilute acid-soluble (CHda) carbohydrates were determined on the soil samples. Also, the specific ?-glucosidase activity (SEA), dispersion ratio (DR), clay dispersion ratio (CDR) and aggregated clay (AC) were calculated. The results indicated the great influence of soil parent material and slope aspect on soil quality indictors. Lower soil temperature and evaporation rate on north-facing slopes have resulted in less organic matter decomposition and, consequently, more organic carbon storage in soil. Also, the soil general fertility is better in north-facing slopes as compared to that in south-facing slopes. The amount of MR, LC2, LC60, CHda, CHhw and CA are higher and that of CDR is lower in soils developed on north-facing slopes as comaper to south aspects. As a result of higher erosion and degradation rate in south-facing slopes, soils on such aspects have lower quantity of clay and higher amount of sand than north-facing soils. Carbonates and pH in soils are mainly controlled by parent material and slope aspect does not seem to play any major role. The higher and the lowest carbonates content and pH were observed in soils from marl and dolomitic limestone, respectively. Due to higher stability, soils derived from dolomitic limestone have higher vegetation cover and rhizospheric activities as compared to soils developed on marl and conglomerate. This appears to have resulted in greater total organic carbon, microbial respiration and soluble carbohydrates in these soils. The amount of labile C, is
