Several lines of evidence have shown that stress has key role in different aspect of physiological process. Relapse to drug-seeking in abstinent morphine addicts and reinstatement in experimental animals are observed when exposed to drug-associated stimuli or cues, the drug itself, and stressful events. However, the effect of forced swim stress (FFS) as a physical stress on the reinstatement of opiate-seeking after extinction has not been fully studied. Therefore, we tried to investigate the effects of FFS in induction of morphine conditioned place preference (CPP) reinstatement. In this present study, the CPP paradigm was done and animal displacement, conditioning score and locomotor activity were recorded by Ethovision software. Forced swim stress was induced by putting the animal in a cylinder filled with water (27 C) for 6 minutes. After 10 minutes, morphine (5mg/kg) was administered subcutaneously and the animal was inserted in to its assigned compartment in CPP box for 30 minutes. All animals underwent extinction sessions until the CPP was extinguished; rats were confined to the previous morphine- or saline-paired compartment for 30 min a day for 8 days. The next day following the last extinction session, morphine CPP reinstatement was induced by FSS as stress-induced reinstatement. In FSS protocol, each animal was put in a cylinder filled with water (23-27○C) and was forced to swim for 6 min. The results showed that FSS could induce reinstatement of morphine CPP. It is supposed that there is a relationship between this model of physical stress and the level of glucocorticoids during forced swim stress protocol in the rats.