Purpose: The objective of this study was to evaluate the feasibility of application of thermoplastic poly-L lactic acid (PLLA) membranes for guided bone regeneration in rabbit parietal bone. Materials and Methods: PLLA membranes with a molecular weight of 100,000 (PLLA-100,000) and a molecular weight of 380,000 (PLLA-380,000) were dissolved in chloroform to prepare concentrations of 8% by weight and 4% by weight, respectively. The compression strength, temperature, and time to prepare each formulation were measured. Moreover, the pH was noted and cytotoxicity of the membrane was determined by monotetrazolium assay. In vivo experiments were performed to measure the volume of newly formed bone tissue in hematoxylin and eosin-stained tissue sections 4 and 12 weeks after implantation. Results: The membrane prepared from PLLA-380,000 showed excellent thermoplasticity at 75°C to 80°C and the compressive strength was equal to that of titanium mesh, in contrast to that of PLLA-100,000 and poly(lactic acid-co-glycolic acid). There was a significant change in the pH of an aqueous solution in which the PLLA-380,000 membrane was placed, but there was no cytotoxic activity. The membrane made of PLLA-380,000 induced new bone formation in a dome shape without any membrane deformation. Conclusion: Thermoplastic PLLA membrane shows promise for guided bone regeneration in vertical bone augmentation. Keywords: bone augmentation, dental implants, guided bone regeneration, membrane, poly(L-lactic acid), thermoplasticity