The present invention relates to a method for preparing a medical material for replacing a hard tissue defect and a medical material produced therefrom. More specifically, in the present invention, powders of bioactive glass are press-molded, and are then subjected to a first heat treatment at a relatively low temperature below the glass transition temperature of bioactive glass. Then, the resultant is processed into a desired shape and then subjected to a second heat treatment at a temperature higher than the glass transition temperature of bioactive glass. Accordingly, the present invention provides a medical material which can be customized to a desired shape of a hard tissue defect in a living body and minimize thermal shock, and which is capable of exhibiting a bone fusion property, while overcoming the low compressive strength drawback of hydroxyapatite, which is an existing hard tissue replacement material currently in use.