The major goals of periodontal therapy are the functional regeneration of periodontal supporting structures already destructed by periodontal disease. There have been many efforts to develop materials and therapeutic methods to promote periodontal wound healing. With the development of non-resorbable membrane, GTR has proved to be the representive technique of periodontal regeneration. However, due to various clinical problems of non-resorbable membrane, resorbable membrane was developed and it showed to be clinically effective. The newly developed Para-Dioxanone membrane has a characteristic of non-woven fabric structures which is different from the generally used membranes with structure of mesh form. In addition, Chitosan membrane has been developed to apply its adventage maximally in GTR. Although a number of different types of membranes had been clinically used, researches on absorption rate of membranes were inadequate and limited to subjective opinions. However, since long term period of resorption and space maintenance are required in implant or ridge augmentation, accurate verification of resorption rate is clinically important. In this study, we had implanted Resolut(R), Biomesh(R), Para-Dioxanone membrane and Chitosan membrane (Size : 4mm ${ imes}$ 4mm) on dorsal side of Sprague Dawley rat, and sacrified them after 4 weeks, 8 weeks, 12 weeks respectively. Histologic observation was carried out, and the following results were obtained by calculating the objective resorption rate. 1. In case of Resolut(R), external resorption took place initially, followed by internal resorption. Surface area are 5.76${pm}$2.37$mm^2$, 4.90${pm}$l.06$mm^2$, 4.90${pm}$0.98$mm^2$ at 4 weeks, 8 weeks, 12 weeks respectively, and invasion rate of connective tissue to membrane are 31.6${pm}$4.5%, 52.8${pm}$9.4%, 56.4${pm}$5.1% respectively. 2. Biomesh(R) showed a pattern of folding, relatively slow resorption rate with small size of membrane. Surface area are 3.62${pm}$0.82$mm^2$, 3.63${pm}$0.76$mm^2$, 4.07${pm}$1.14$mm^2$ at 4 weeks, 8 weeks, 12 weeks respectively, and invasion rate of connective tissue to membrane are 26.1${pm}$5.8%, 30.9${pm}$3.4%, 29.2${pm}$3.6%, respectively. 3. Para-Dioxanone membrane was surrounded by fibrous conncetive tissue externally, and resorption took place internally and externally. Surface area are 5.96${pm}$1.05$mm^2$, 4.77${pm}$10.76$mm^2$, 3.86${pm}$0.84$mm^2$ at 4 weeks, 8 weeks, 12 weeks respectively, and invasion rate of connective tissue to membrane are 30.7${pm}$5.1%, 53.3${pm}$4.4%, 69.5${pm}$3.1%, respectively. 4. Each fiber of Chitosan membrane was surrounded by connective tissue and showed external resorption pattern. It showed little invasion of inflammatory cells and excellent biocompatability. The resorption rate was relatively slow. Surface area are 6.01${pm}$2.01$mm^2$, 5.49${pm}$1.3$mm^2$, 5.06${pm}$1.38$mm^2$ at 4 weeks, 8 weeks, 12 weeks respectively, and invasion rate of connective tissue to membrane are 31.3${pm}$3.6%, 38.4${pm}$3.80%, 39.7${pm}$5.6%, respectively. Consequently, Para-Dioxanone membrane and Chitosan membrane are found to be clinically effective for their excellent tissue reaction and biocompatibility. Futhermore, the advantage of bone regenerating ability as well as the relatively long resorption period of Chitosan membrane, it might be widely used in implant or ridge augmentation.