Finding a right repair material for furcation perforation is one of the major issues in clinical endodontics. In this experiment, three materials, calcium sulfate, amalgam, and calcium hydroxide were tested for perforated furcation repair. Sixty premolars and molars of five dogs were used. A #4 round bur was used to create the perforation. All experimental teeth were divided into two repair-time groups. One was immediate-repair group, where the perforation was repaired immediately, the other was delayed-repair group, where the perforation was left open for four weeks and then repaired with the same manner as in the immediate-repiar group. All chamber openings were sealed with amalgam and then radiographed. The animals were sacrificed at eighth week following the repair procedure. Radiographic evaluation for furcal bone destruction was done. Histologic evaluation was ranked as 0,1,2,3 according to the inflammation degrees. New bone formation was also recorded. The following conclusions were drawn within the limits of the experimental results: 1. In immediate-repair group, no significant differences existed between the materials. 2. In delayed-repair group, calcium sulfate showed significantly less furcal bone destruction and lower inflammation degree than amalgam.(p<0.05) 3. Overextruded specimens showed more severe inflammation than unextruded specimens. 4. Most of the specimens showed certain degrees of inflammatory reaction and incomplete hard tissue healing. 5. In delayed-repair group, treated group showed less inflammation than untreated control group.