This invention provides organic/inorganic composite biomaterials constituted by composites of hydroxyapatite and collagen and having an average fiber length of 60 μm or longer, and a process for producing the same in which the calcium ion and phosphate ion concentrations in the reaction vessel are optimized through regulation of the concentration of a starting material and the flow rate. The organic/inorganic composite biomaterials have mechanical strength and a biodegradation rate suitable for artificial bones through the introduction of crosslinking therein.