Dehiscence bone defects, frequently observed on dental implants placed in periodontitis-affected alveolar bone or extraction sockets were treated with β-tricalcium phosphate (β –TCP) and chitosan membrane for guided bone regeneration, and the new bone formation on the treated sites were studied. Beagle dogs were used for the experiment. First to fourth mandibular premolars were extracted, and the post extraction alveolar bone surface was planed. After 8 weeks of healing, 3 by 4mm dehiscence defects were created using straight fissure burs. Total of 16 oxidized titanium surface implants were placed on the bone defects of the subjects, two on each side. Control sites were treated with implants only. Experimental Group 1 sites were treated with implants and chitosan membrane. Experimental Group 2 sites were treated with implants, β-TCP and chitosan membrane. Experimental Group 3 sites were treated with implants, β-TCP, autogenous bone and chitosan membrane. The animals were sacrificed 12 weeks after implant placement, and the specimens from the treated sites were histologically studied with following results. Limited amount of new bone formation was observed in control group with unexposed membrane. Slightly greater amount of bone formation was observed on sites treated with β-TCP+membrane or autogenous bone+ β-TCP+membrane compared to control group. Remnants of chitosan membrane and β-TCP encapsulated with connective tissue were observed during experimental periods. These results suggest that further studies are needed on membrane rigidity and infection control for space maintenance underneath the membrane and bone substitutes in the treatment of dehiscence defects.