To evaluate the role of botulinum toxin type A (BTX-A) in the treatment of pain associated with nocturnal bruxism. Fifty subjects reporting nocturnal bruxism were recruited for a randomized clinical trial. Twenty five bruxers were injected with botulinum toxin in both masseters, and twenty five were treated with traditional methods of treating bruxism. Patients were evaluated at 3rd week, 2nd and 6th month and one year after injection and then used to calculate bruxism events. Bruxism symptoms were investigated using questionnaires. Mean pain score due to Bruxism events in the masseter muscle decreased significantly in the botulinum toxin injection group A (P =0.000, highly significant). However, in the conventional treatment group, mean pain score does not show improvement with time (p>0.05). Our results suggest that botulinum toxin injection reduced the mean pain score and number of bruxism events, most likely by decreasing the muscle activity of masseter rather than affecting the central nervous system.