Laser photobiostimulation (LPBS) is one of the recent additions to therapeutic procedures used in chronic pain management. Though widely used, a clear understanding of its mechanism of action was not disclosed. In addition, the energy density that produces maximal benefit has not yet been established. The purposes of this study were to determine the effects of LPBS on pain relief in rat and to determine treatment dosage. Eight, 8-week old female, Sprague-Dawley rats were employed. All subjects were assigned to one of four groups: a sham laser group, a 0.4 $J/cm^2$ laser group, a 2.0 $J/cm^2$ laser group, and a 6.0 $J/cm^2$ laser group. Ga-As laser (904 nm wavelength) of three different energy densities (0.4, 2.0, 6.0 $J/cm^2$) was applied on a tail acupuncture point and tail-flick latencies were measured five times pre-and post-treatment as following schedules: 30 minutes, 1 hour. 24 hours. 48 hours, and 7 days later. An increase in pain threshold was demonstrated following LPBS, employing rat tail-flick test. LPBS of 2.0 $J/cm^2$ produced hypoalgesia of rapid onset and short duration (1 hour, 24 hours) while the response to 6.0 $J/cm^2$ was delayed and lasted longer (48 hours, 7 days). LPBS of 0.4 $J/cm^2$ did not produce any hypoalgesia.