One of the major problems in modern dentistry is the recovery of bone defects. The aim of this prospective experimental study was to evaluate the effect of light-emitting diode (LED) photobiomodulation therapy on bone healing of rat calvarial defects. Twenty-eight male Sprague Dawley rats were used for the study. Critical size defects with 5 mm diameter were made with a trephine bur used in a low-speed handpiece under continuous sterile saline irrigation on each side of the sagittal suture. All critical size defects on the right side were filled with corticocancellous bone graft material and all the defects on the left side were left empty. The animals were randomly divided into two groups of 14 rats each. Group I received LED therapy and Group II did not receive any therapy. OsseoPulse (R) LED device (Biolux Research Ltd.) 618 nm wavelength and 20 mW/cm(2) output power irradiation was started immediately after the surgery and was applied for 20 minutes at 24-h intervals for 7 and 14 days. In each group, seven rats were sacrificed on the 8th day and the remaining rats were sacrificed on the 15th day. Bone healing of the non-grafted side was statistically significant in Group I on both 8th day and 15th day; on the other hand, in the grafted side, enhanced bone healing was dominantly observed on the 15th day in Group I, compared to Group II, although the difference was not significant. Within the limits of this study, the findings suggested that LED therapy might have a favourable effect in the early phase of bone healing.