The present invention relates to a porous biomaterials surface activation method by coating with a layer of apatitic nanocrystals in order to increase their surface reactivity. The method according to the invention is characterized by the following steps: a) preparing a nanocrystalline apatitic calcium phosphate analogous to bone mineral by mixing a calcium salt solution with a phosphate salt solution in a Ca/P ratio ranging between 1.3 and 2 at a temperature ranging between 0 and 60 ° C., b) slurrying the mixture obtained in step a) in an aqueous solution so as to obtain a fluid, homogeneous paste containing 80 to 98% of water, c) bringing a porous biomaterial into contact with the suspension obtained in step b), d) drying the porous biomaterial at a temperature below 100 ° C.