Objective: Bone grafts have been widely used in osseous defects in medicine and dentistry (e.g. periodontology, implantology). This study aims to assess bone and tissue response to a xenograft (Unilab Surgibone) after the first and third month of implantation and its cytotoxicity in vitro. Material and Methods: Fifteen rats, each of which having a 5 mm critical-size, symmetrical, circular defects in the corpus of the mandible were recruited. The experimental defects were filled with the biomaterial whereas defects on the opposite side were used as controls (sham-operated group). After histological follow-up, serial sections were prepared for evaluation under light microscope. The cytotoxicity of xenograft was examined in vitro. Result: Xenografts did not show any cytotoxicity for the cells. There was no callus formation in the implantation site at the first and third months, and Unilab Surgibone material was surrounded with fibrous tissue. Dense collagenous tissue was observed in the control site at the first and third months. Conclusion: Although there was no evidence of bone building, the biomaterial seems biocompatible and can be considered as a space filler for such applications in dentistry.