The purpose of this study was to analyze comparatively the effect of various root pretreatments prior to delayed replantation. Total 6 beagle dogs were used for the experiment and 8 teeth per each animal were treated by several prepared regimens before replantation. After 3 & 6 weeks of experimental periods, animals were sacrificed by perfusion method. The results obtained from the present study can be summarized as follows: 1. All root pretreatment regimen used in this experiment showed effectiveness in the periodontal repair of delayed replanted teeth. 2. The teeth treated by the regimen of stannous fluoride combined with tetracycline revealed more favorable tissue response and less frequent root resorption or ankylosis than other groups. 3. The long term effect of Group IV-regimen seems to be worth further study since the result at 6-weeks showed the significant progress in periodontal healing when compared to 3-week result which was not indicated in any other group