The distribution of the clay minerals of the argillaceous fraction of the bottom sediments of Todos os Santos Bay reflects the climatic condition, the constitution of the rocks, and the weathering products of the region. Based on the distribution and on the source of the clay minerals, the area can be divided into three parts: a) Northern region, of low energy where the argilaceous sedimentation is more intense and derives mainly from the erosion of the nearby sedimentary rocks. Kaolinite predominates slightly over illite, whereas the montmorillonite is present in subordinated amounts; b) Southern region of relatively high energy. The argillaceous sedimentation is rare and influenced by the material brought from the oceanic regions. Kaolinite predominates in excess of 50% of the total amount of the clay minerals; c) Region of influence of the Paraguaçu River. Kaolinite is the main clay mineral, and montmorillonite predominates over illite. The mineralogy of the clay minerals controls the distribution of Si, At, K, and Mg. The distribution of Ca and Sr is related to the fine-grained biodetritic material present in the clay fraction. The relatively high content of Fe results from the intense action of the chemical weathering in the source area. The elements Cu, Ni, Cr, and Zn occur adsorbed on the surface of the clay particles. Relatively high concentrations of Zn in some areas probably result from the pollution by industrial wastes.The distribution of the clay minerals of the argillaceous fraction of the bottom sediments of Todos os Santos Bay reflects the climatic condition, the constitution of the rocks, and the weathering products of the region. Based on the distribution and on the source of the clay minerals, the area can be divided into three parts: a) Northern region, of low energy where the argilaceous sedimentation is more intense and derives mainly from the erosion of the nearby sedimentary rocks. Kaolinite predominates slightly over illite, whereas the montmorillonite is present in subordinated amounts; b) Southern region of relatively high energy. The argillaceous sedimentation is rare and influenced by the material brought from the oceanic regions. Kaolinite predominates in excess of 50% of the total amount of the clay minerals; c) Region of influence of the Paraguaçu River. Kaolinite is the main clay mineral, and montmorillonite predominates over illite. The mineralogy of the clay minerals controls the distribution of Si, At, K, and Mg. The distribution of Ca and Sr is related to the fine-grained biodetritic material present in the clay fraction. The relatively high content of Fe results from the intense action of the chemical weathering in the source area. The elements Cu, Ni, Cr, and Zn occur adsorbed on the surface of the clay particles. Relatively high concentrations of Zn in some areas probably result from the pollution by industrial wastes.