The ability of ethylamine to influence hydroxyapatite (HAp) crystal growth has been studied. HAp crystals were obtained from the mixture of HAp precursor slurry and various amount of ethylamine under hydrothermal condition. The products synthesized with 5 wt% or more ethylamine were plate-like crystals whose grown face was a-plane of HAp. Several analyses suggested that the role of ethylamine was the inhibition of crystal growth along a particular axis.