Here we reported a method to simultaneously control the particle size and morphology of alpha-CaSO4 center dot 1/2H(2)O (alpha-HH) prepared from flue gas desulfurization gypsum by adjusting the succinic acid concentration and glycerol content under mild conditions. Succinic acid controlled the crystal morphology by adsorption onto alpha-HH surfaces, and glycerol controlled the crystal particle size, in which an increase in the maximal relative supersaturation (S-max) and nucleation rate of alpha-HH was hypothesized to cause the change in alpha-HH particle size. Then, based on the method, alpha-HH with different particle sizes but with almost the same morphology was prepared, and the influence of the crystal particle size on the mechanical strength of the alpha-HH pastes was explored. With decreasing alpha-HH particle size from about 26 to 5 mu m, the dry compressive strength of the pastes made from the alpha-HH decreased remarkably from 68.02 to 34.85 MPa, which was ascribed to an increase in the internal porosity of the pastes.