Abstract: Disclosed is a method for producing a collagen/apatite composite membrane useful as a barrier to protect fibrous connective tissues from infiltrating into a site of defective tissue or bone in guided tissue regeneration (GTR) or guided bone regeneration (GBR) procedures. Such composite membrane can be obtained by the steps of co-precipitating collagen and apatite in aqueous basic solution in a very well controlled manner, followed by casting the precipitation onto a filter paper, lyophilization and cross-linking. The method according to the present invention can allow forming a collagen/apatite composite membrane in which the crystals of apatite, in particular, hydroxyapatite are coated on and along with the collagen fiber direction without aggregation of self-assembled collagen fibers. Such composite membrane has excellent biological and mechanical properties such as biocompatibility, cell affinity, biodegradability and form stability, and therefore it can be used as a barrier for GTR.