Purpose: The aim of this study was to qualitatively evaluate a poly(lactic acid-co-glycolic acid-co-ε-caprolactone) (PLGC) membrane as a barrier for guided bone regeneration in the canine mandible and to compare it to a nonresorbable polytetrafluoroethylene (PTFE) membrane. Materials and Methods: Two wedge-shaped bone defects were created bilaterally in the mandibles of 12 beagle dogs. The bone defects in the left mandible were divided into three groups and treated as follows: PLGC membrane alone, PLGC membrane plus autogenous cortical bone chips, and titanium-reinforced expanded PTFE (TR-PTFE) membrane. The bone defects in the right mandible of each animal were left without membranes as a control. Computed tomography (CT) was performed at 3 and 6 months postoperative to evaluate bone regeneration. After a healing period of 6 months, the mandibles were removed en bloc for micro-CT and histologic analyses. Results: CT analyses at 3 and 6 months showed that there was significantly more bone augmentation at all experimental sites than at the control sites. The volume of bone at defect sites covered with TR-PTFE was significantly greater than at defect sites covered with PLGC membrane with or without autogenous cortical bone. Micro-CT measurements showed that the volume of new bone formed at sites covered with TR-PTFE was significantly greater than at sites covered with PLGC membrane. However, the density of new bone was significantly higher at sites covered with PLGC membrane, with or without cortical bone, than at sites covered with TR-PTFE. Histologic analysis verified the presence of well-vascularized loose connective tissue in the pores of the PLGC membrane. Conclusions: Compared to TR-PTFE, the macroporous bioresorbable PLGC membrane did not significantly increase the amount of new bone in defect sites, but it facilitated the regeneration of mature bone. Schlagwörter: guided bone regeneration, lateral ridge augmentation, poly(lactic acid-co-glycolic acid-co-ε-caprolactone), titanium-reinforced expanded polytetrafluoroethylene membrane