The aim of the present study was to evaluate the response of surrounding tissues to newly developed poly(trimethylene carbonate) (PTMC) membranes. Furthermore, the tissue formation beneath and the space maintaining properties of the PTMC membrane were evaluated. Results were compared with a collagen membrane (Geistlich BioGide), which served as control. Single-sided standardized 5.0 mm circular bicortical defects were created in the mandibular angle of rats. Defects were covered with either the PTMC membrane or a collagen membrane. After 2, 4 and 12 weeks rats were sacrificed and histology was performed. The PTMC membranes induced a mild tissue reaction corresponding to a normal foreign body reaction. The PTMC membranes showed minimal cellular capsule formation and showed signs of a surface erosion process. Bone tissue formed beneath the PTMC membranes comparable to that beneath the collagen membranes. The space maintaining properties of the PTMC membranes were superior to those of the collagen membrane. Newly developed PTMC membranes can be used with success as barrier membranes in critical size rat mandibular defects.