Abstract: Freshwater pearl oysters were exposed to different concenthetions of copper sulfate (7,15, and 1.5mg / 1) for different days (7,15, and 35d). The luminosity of pearls was affected obviously by copper sulfate, and the percentage of prismatic pearls increased with the increase of copper sulfate concentrations and over the time. When exposed for 35d, the shape and ultrastructure of epithelial cells in mantle and pearl-sac were influenced or even damaged, and the degree of such damage increased more significantly when the copper sulfate concentration reached or exceeded 1.0mg / L.