Aim: This study was conducted to examine the effect of granulocyte colony stimulating factor (G-CSF) on the number of neutrophils and on the histopathological changes of inflamed pulpal and periodontal ligament in neutropenic rats. Methods: It was conducted on 64 adult male albino rats of average body weight 200-250 gm. The effect of G-CSF on changes in pulpal and periodontal tissues was investigated at 2, 4, 7, and 10 days after pulpal exposure of the mandibular first molar,also after experimental periodontitis of the mandibular incisors of normal rats and of those with methotrexate-induced neutropenia. Results: In untreated rats, G-CSF significantly (P < 0.05) increased the number of peripheral neutrophils but didn't affect pulpal or periodontal inflammation. In methotrexate induced neutropenic rats, the number of neutrophils reduced, and the area of pulpal and periodontal ligament necrosis enlarged. After the G-CSF injection, the decreases in neutrophil count significantly (P < 0.05) reversed, and the enlargement of pulpal and periodontal ligament necrosis inhibited. Conclusions: These findings indicate that G-CSF prevented the reduction in neutrophils number,function and reduced the pulpal and periodontal necrosis observed in the neutropenic rats, and suggested that neutrophils defend against bacterial invasion in pulpal and periodontal tissues.