Wet grinding of diatomite was carried out in a stirred mill. The changes in particle size, specific surface area and structure or the particle shape in the wet grinding process were investigated. The adsorption of methylene blue from aqueous solution by the ground diatomite was also studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and IR spectra were employed to characterize the ground diatomite. The median particle size decreased and the specific surface area increased with the grinding time, an agglomeration phenomenon was not observed during the experimental grinding time. The X-ray diffraction patterns versus grinding time showed that a peak intensity reduction of opal. The results of adsorption of methylene blue onto diatomite indicated the adsorption capacity increases with the increase of grinding time until eventually reaches a constant value.