The effect of cetyltrimethylammonium bromide (CTAB) on the crystal morphology and size of calcium sulfate whiskers in aqueous HCl solutions was investigated by combined experimental and molecular dynamics (MD) simulation studies. When CTAB was used, calcium sulfate whiskers with small diameters and high aspect ratios were obtained. The MD simulation results indicate that the experimental results can be attributed to the combined effect of the surface adsorption and inhibition of the solute diffusion of CTAB.