The southwestern region in Saudi Arabia is located within Al-Sarrawat high elevation mountains. In these mountains the dominant igneous and metamorphic rocks (granite, basalt, diorite, gabro, mica-schist and others) was relatively high leading to the formation of weathering products rich in amorphous materials, particularly in the residual soil profiles. The main types of parent materials in the study area are residuum in the soils formed in-situ from the source rock particularly at mountains. alluvium and colluvium particularly in slopes. The present study aimed to evaluate soil characteristics. the content and distribution of amorphous silica and alumina and free iron oxides of soils developed on different parent materials (Le. igneous and metamorphic rocks) in the southwestern region. Saudi Arabia. This investigation also aims to test the impact of amorphous materials on some soil characteristics. Results showed that the studied soils are differing considerably in their characteristics and morphological features, these differences are mainly related to variation in parent materials, elevation, climatic conditions and vegetation cover. The free iron oxides (Fed) (9.8 - 14.6 %) is the largest components forming the amorphous materials in all the studied soils followed by amorphous Siam (0.1 — 8.4%) and Al (Alam) (0.1 — 9.2%) in some soils or in the others. Distribution of these components with depth indicated no specific depth wise distribution trend in most cases. Contents of amorphous inorganic materials in soils are mainly associated with the parent rock from which these soils are derived. Thus. soils derived from metamorphic rocks (schist) have amorphous inorganic materials more than these derived from igneous rocks (granite and basalt). There is no direct correlation between some soils characteristics and the amorphous inorganic materials. This may be attributed to the effect of environmental conditions in the studied area on these relationships.