The current study aimed to evaluate the effectiveness of photobiomodulation therapy for the prevention of incidence of alveolar osteitis (AO) and postoperative pain following third molar surgery. In this double-blind clinical trial, the impacted teeth of patients having bilateral impacted mandibular third molars were surgically extracted; for each participant, one socket was randomly assigned to receive photobiomodulation treatment, the other received sham treatment. 660 nm 200 mW CW was applied at a distance of ~1cm to 4 points on the occlusal area of extraction socket (beam area at the tissue ~0.64 cm 2 , 312.5 mW cm -2 , 1J, 1.6 J cm -2 ). Also, 810 nm 200 mW CW was applied at tissue surface at three points on the buccal and three points on the lingual gingiva, for 15 s (400 mW cm -2 , 3 J, 6 J cm -2 ). There was a statistically meaningful difference in AO frequency between the two groups, and the photobiomodulation group showed lower AO frequency compared with the sham PBM treatment (P-value = 0.035). According to the findings of this study, photobiomodulation therapy reduced the incidence of AO following surgical removal of impacted mandibular third molars. The incidence of AO typically occurs 3-7 days post-extraction, and our results suggest that PBM treatment within the 7 days could help reduce the risk of AO development.