The purpose of this study is to evaluate the effects of bioresorbable membranes in guided bone regeneration of streptozotocin induced diabetic rats. 50 Sprague-Dawley rats were randomly categorized into 4 groups: Group 1 & 2 had 10 normal rats each and group 3 & 4 included 15 streptozotocin induced diabetic rats each. Defect measuring 7mm in diameter was formed on every rat calvarium. No membrane was used in groups 1 & 3 and membranes were used in groups 2 & 4. The rates were sacrificed at 2 and 4 weeks after defect formation. Routine histological specimens were prepared. Masson-trichrome and HE stain were done before light microscopy. Guided regenerative potential was evaluated by measuring the amount of new bone formation in the calvarial defect by histomorphometry. Following results were obtained. 1. New bone formation in the diabetic groups was significantly less that than in the normal groups regardless of membrane use(p<0.05). 2. In the comparison of new bone formation in the normal groups, membrane group showed significantly more bone formation(p<0.1). 3. When the amount of new bone formation was compared in the diabetic groups, more bone was formed in the membrane groups but the difference was not statistically significant.4. In the normal groups the amount of new bone formation was significantly greater at 4 weeks compared to that at2 weeks(p<0.05) but amount of bone regeneration at 4 weeks was not significantly greater than that at 2 weeks in both diabetic groups.