Abstract： Objective To investigate the role of pulp in the root resorption of primary teeth without permanent tooth germs. Methods The animal model without permanent tooth germs was established by surgery in Beagle dog. The root resorption was observed by taking periapical radiographs periodically. The samples of mandibular bone and pulp at different resorption stages were collected. The distribution of odontoclasts and the activating factor was analyzed by histological staining and semiquantitative reverse transcriptase polymerase chain reaction(RT-PCR). The role of pulp in the root resorption of primary teeth was tested by early pulpectomy. Results In the root resorption of primary molars without permanent teeth germs, a large number of odontoclasts were present on the pulpal surface of the root canal. Semiquantification RT-PCR showed that the ratios of the expression of receptor activator of NF-κB ligand (RANKL) mRNA and β-actin in the pulp of permanent teeth and primary teeth without permanent teeth germ during different periods of root resorption are 0. 1314, 0. 1901, 0. 2111 and 0. 6058 ( P ＞ 0. 05 ). The root resorption of primary teeth without permanent teeth germs in test groups was about 5 weeks later than that of control group. Conclusions The pulp of primary tooth played an important role in the root resorption of primary tooth without permanent tooth germ.