The aim of this study was to investigate the histological changes of dental pulp following luxation of tooth, and compared with that of pulp exposure mechanically. Upper left first molar of twenty male, 5 weeks age, Wister rats were used for this study; ten were used for trauma group by luxation and ten for mechanically expose group. In trauma group, teeth were luxated using special forceps, and pulp expose groups were exposed by #1/2 round bur with water spray and left alone. Five rats from each group were sacrificed under anesthesia one week following treatment and the remaining 5 rats from each group were sacrificed after two weeks in the same manner. Thereafter 5µm thickness paraffin sections were prepared and stained with haematoxylin -eosin. All sections were observed by light microscopy. In the trauma group 2 weeks following operation, pulp necrosis and formation of bone-like materials in it were seen. While in the mechanically pulp expose group, There were no bone-like materials in the pulp. Therefore bone-like materials in the pulp after necrosis might be related to the strong damage in a short period such as luxation.