Abstract: Root resorption is a physiologic event for the primary teeth, involving the tissue change of alveolar bone and dentin, the cellular change of osteoclasts and odontoclasts, also kinds of cytokines. The stellate reticulum and the dental follicle of the underlying permanent tooth seems to be important for the deciduous root resorption. However, primary teeth without a permanent successor eventually exfoliates as well. Our current understanding on the underlying mechanisms is slim. This article summarizd the research progress on the mechanisms of physiologic root resorption in primary teeth.