The dissolution kinetics of the (010) face of dicalcium phosphate dihydrate crystals in a physiological solution were investigated by ipl situ atomic force microscopy. Although many etch pits with 0.75 nm high elementary steps were formed, spiral dissolution was hardly ever observed. Step velocity showed strong dependence on the crystallographic orientation and decreased with decrease of the interstep distance. From the ratio of the step kinetic coefficient to the characteristic diffusion rate, it was concluded that the dissolution process under the present conditions was controlled by detachment of molecules at a step front and surface diffusion.