Natural clay minerals have attracted attention for their availability and economical cost as adsorbents in the treatment of contaminants in aquatic environments. In this study, Truc Thon white ball clay from Hai Duong province, Vietnam was activated by different acids including H₂SO₄, HCl and H₃PO₄ at 110^°C from 6 to 18 hours under refluxing conditions. The chemical composition and structure changes before and after the activation of the clay were characterized by X-ray fluorescence, X-Ray Diffraction and Fourier transform infrared spectroscopy. The raw clay is mainly composed of minerals containing alumina and silica while in activated clay, silica is dominant in amorphous phase. The specific area of clay particles was increased significantly after acid treatment from 10.55 m².g^-1 to 178.53 m².g^-1. Images from a scanning electron microscope also reveal more porous structure of activated clay. These behaviors make acid activated clay highly effective in various adsorption applications.