The effect of an emulsion medium on the morphology and size of hydroxyapatite (HAp) nanoparticles was investigated. The HAp particles prepared in a pentaethyleneglycol dodecylether emulsion were smaller in size and in aspect ratio than those prepared from a non-emulsion. Morphological difference was also observed between the products prepared in the two systems. The edges of the HAp particles derived from the emulsion system were curved and rounded while those in the non-emulsion system were straight and truncated. These differences, deriving from the reaction media employed, indicated that a template effect of the emulsion can be utilized for controlling the size and habit of HAp nanoparticles.