A study on Micromorphology and Relationships between Phosphate Adsorption and Some Properties of Soils in Khao Kho Area, Changwat Petchabun was carried out on selected representative areas within the boundaries of three Royal Forestry Department Centers. Field analysis of soils emphasized on pedon analysis. Laboratory study included analysis on physico-chemical properties, mineralogical and micromorphological characteristics and experiment on phosphate adsorption of soil samples. Results of the study revealed that the soils include six Alfisols and five Mollisols. Their parent materials consisted of colluvium, short-distance transported local alluvium and residum dervied from rhyolitic tuff, andesitic tuff, rhyolitic-andesitic tuff, rhyolite and andesite. Their texture ranges from silt loam to caly, They have moderately well to excessive drainage. The soils have good physical properties with low to moderate bulk density (1.05 - 1.51 Mg m(-3)) and high available moisture. Alfisols have lower pH, organic matter, total nitrogen, available phosphorus and potassium, extractable bases, cation exchange capacity, percentage base saturation, and extractable iron and manganese, but higher extractable, acidity than that of Mollisols. Their electrical conductivity and extractable aluminium are low and not observadly different. Kaolinite dominates clay fraction of both soils. Other clay species include mainly vermiculite and smectite. Alfisols show higher amount of kaolinite but lower amount of vermiculite and smectite than does the Mollisols. Quartz dominates their silt fraction. Other minerals are feldspar, goethite, hematite and gibbstie. Alfisols have higher amount of quartz but lower amount of feldspar than that of Mollisols. Micromorphologically, angular and subangular quartz grains are the dominant skeleton grains in these soils. Other features include vesicular vughs, channel and tubular pores and small amount of rion and manganese oxide nodules. The coarse/fine relationship in the fabric in generally porphyroskelic plasmic but Alfisols have the higher coarse/fine ratio than that of Millisols. In Alfisols, clay coatings on skeleton granis are quasi-coatings of ferri argillan whereas the same materials of coating in Mollisols are in hypo-coating type. Thin clay coatings on pore walls can be observed in both Alfisols and Mollisols. The micromorphological features of these soils indicate a more advanced development stage of alfisols. These soils have low pholphate adsorption (15.5-86.0 mg kg(-1)). They have highly significant direct correlation between phosphate adsorption and amount of clay, extractable aluminium but they have highly significant inverse correlation of phosphate adsorption to soil reaction, organic matter, total nitrogen, available phosphorus and potassium, extractable bases, cation exchange capacity and percentage base saturation. Phosphate adsorption is higher in Alfisols that that in Mollisols due to the lower pH and organic matter and higher kaolinite in Alfisols. In general, alfisols have lower fertility than Mollisols do and their internal propeties are less adverse for agricultural land use than the steep slope nature of the areas.