Abstract: The pupil size of both human and other animals can be affected by light Many kinds of psychiatrical and psychological disorders associate with abnormal properties of pupil light reflex Thus, the properties of pupil light reflex function can reflect these kinds of mental disorders However, the effect of drug of abuse on pupil light reflex function is till unclear To quantificationally assess the effects of addictive drugs on pupil light reflex function, in the present study, we examined the effects of morphine on pupil diameter and pupil light reflex function in rhesus monkeys We measured the pupil diameter at different timing points after during morphine administration We found that morphine administration reduced the diameter of pupil and decreased the constriction rate Our present results provide an experimental support for applying pupil light reflex property as a reference in addicts’ detection.