Introduction: Alzheimer's disease (AD), the most common cause of dementia among older people, gradually destroys memory and learning skills, and eventually the ability to carry out all tasks. In most people with AD, symptoms first appear after age 60. Materials and Methods: The experiments were carried out in adult (6-7 months old) male Wistar rats (230-270 g) in 3 groups of control, sham and Streptozocin (STZ). Animals in sham and STZ groups received normal saline and STZ intraventricular injections for two days, respectively. To assess spatial memory 8, 18, 30, 45, 70, 90 days after STZ injection, passive avoidance test was performed. Results: The mean retention latency decreased in STZ groups compared to control and sham groups. According to our findings, the most serious short-term and long-term memory loss was observed 90 days after STZ injection. The long-term memory destroyed earlier than short-term memory in STZ treatment rats. Conclusion: STZ injection in rats was resulted in significant time-dependent damages of cognitive abilities.