Objictive To investigate the restorative procedure,and the survival period of the mandibular poste riorresidual crown companied with penetrate dpulp floor after eomplet eendodontie treatment. Method 95 patients (113teeth) with penetrated pulp floor of mandibular posterior residual crowns were selected at random .All the eases were followed up from haft a month to a month after excellent root canal therapy and without any uncomfortable symptom. Then,these mandibular residual teeth were separated into medial part and distalone along the root furcafion,and modified each part in 2 to the shape of premolar by post/core crown,meanwhile the two post/core crowns of each posterior residual tooth were repaired by combination casting crowns.Result All the patients were followed up for five years after prostheties treatment .It was found that the valid rate was87.7%,and these teeth can performed their mormal function.Conclusion This treatment may be employed as a practical means for the mandibular posterior residual crown with penetrated pulp floor. Key words: Penetrated pulp floor; Mandibular posterior residual crowns; Observation treatment; Post/cord combination casting crown