Pisolitic-oolitic-type bauxite is one of the main types of sedimentary bauxite. Pisolites (ooids) are mainly composed of aluminum-containing minerals such as diaspore and clay minerals, which are closely related to aluminum mineralization. However, the formation mechanism of pisolite (ooid) is not yet clear. This research conducted mineral petrographic and geochemical characteristics on the pisolite (ooid) from Western Guangxi, analyzing the morphological characteristics and elemental composition of diaspore in pisolitic (oolitic) bauxite, and exploring the genesis of pisolite (ooid) and metallogenic mechanism of bauxite. The observation results of petrology show significant differences in the morphology and distribution characteristics of diaspores in the ooids of sedimentary bauxite from Western Guangxi. Based on these differences, the ooids can be divided into six types. The results of the SEM-EDS and EPMA analysis showed that Fe, Si, Ti, and other elements generally existed in the diaspore. Anatase is closely associated with diaspore. There were no signs of metamorphism in the roof and bottom wall-rock limestone of ore-bearing bauxite ore in Western Guangxi, which indicated that the genesis of the diaspore was simple crystalline. The morphological characteristics and chemical composition of the diaspore at the ooid core→ ooid circle layer → ore matrix are different, as well as the lithological features such as a large number of broken pisolites (ooids), directional arrangement of ooids and clastics, dry shrinkage cracks and plastic deformation of ooids. These indicate that the ooids in sedimentary bauxite in Western Guangxi are of colloidal origin and have undergone mechanical transformation. The formation of ooids in Western Guangxi went through four stages: material preparation, hydrolysis of clay minerals, formation of ooid core, and formation of ooid circle layer. It is formed by the weathering of aluminosilicate material to form clay minerals, which further hydrolysis of clay minerals condenses and precipitates to form ooids. The Si-Al ratios (SiO2/Al2O3; 0.02~0.35), ore Chemical Index of Alteration (CIA; 94.41~99.96), Index of Compositional Variability (ICV; 0.07~0.74) analysis results show that the pisolitic (oolitic) bauxite has undergone intense chemical weathering and is the product of intense weathering leaching. The formation of sedimentary bauxite in Western Guangxi is related to leaching and colloid processes, and the bauxite has undergone different degrees of transformation after formation.