Abstract: Opioid abuse is an increasing problem worldwide and the reinforcing effects of opioid analgesics make them susceptible to diversion and illicit use and abuse. As morphological changes in different parts of the brain including the hippocampus and dentate gyrus that have Plasticity is looking for a lot of drug injection in human and animal studies has been viewed. Also other evidences have shown that Astrocytes actively participate in synaptic plasticity. Therefore the aim of this study was obtain of Conditioning Place Preference (CPP) on cell density (Astrocytes number) of rat hippocampal formation. In present study, 48 male Wistar rat weighted average 220-250 g were used. For behavioral tests, rats divided into eight groups and experimental groups daily (three days) received morphine at different doses (2.5, 5, 7.5 mg kg-1) by subcutaneous injection and sham groups, received saline dose (1 mL kg-1) and then CPP test in them were investigated. 48 h after behavioral testing animals were decapitated under chloroform anesthesia and their brains fixed and after tissue processing, slices stained with GFAP immunohistochemistery techniques. Present results showed the most dose responses of morphine were observed in 7.5 mg kg-1. It also revealed that don't exist any differences between the number of astrocytes in CA1 and CA3 in control group and control-saline, but this difference between control and the other groups was significant statistically (p<0.05). We concluded that the phenomenon of morphine based conditioned place preference can cause a significant increase in the number of astrocytes in experimental groups with compared to controls.