The purpose of this study was to evaluate biocompatibility of a new injectable root canal sealer. The cytotoxicity of zinc oxide-eugenol cements, CCQ and the new injectable root canal sealer were assessed by the MTT assays. These materials were filled into the root canals of the dog. One month later, the dog was sacrificed and the X-ray photos were taken. The histological response was observed through the microscope. The results show the new injectable root canal sealer showed better biocompatibility than the other two materials.