Abstract: Abstract Objective To study the expression of TLR4 in rat pulpitis model induced by endotoxin (LPS) so as to evaluate the possible role of TLR4 in rat pulpitis and conjecture its significance in the development of pulpitis. Methods Make the slides of rat molar pulpitis tissue induced by LPS, and examine the expression of TLR4 in rat pulpitis immunohistochemically. Results 1d group: TLR4 was moderately positive in odontoblasts and moderately to stongly positive in the pulp fibroblasts. 3~7d group: the positive expression reduced in odontoblasts and pulp fibroblasts. 2 weeks group: necrosis expanded and was homogeneously weakly positive; odontoblasts, pulp fibroblasts and endothelial cells reduced and were positve; reparative dentin was weakly positive. 3 weeks group: most of the necrosis was homogeneously weakly positive. Conclusion TLR4 is dynamically expressed in the generation and development of rat pulpitis. TLR4 may take part in the regulation of generation, development and repair of pulpitis.