Inhibition of protein synthesis has been shown to affect long-term memory in a wide variety of animal species. But little is known regarding the neuroanatomical location of protein synthesis in different memory tasks. In this study, the effect of intrahippocampal injection of anisomycin, an inhibitor of brain protein synthesis on spatial memory was examined in Morris Water Maze. At first, rats were connulated bilaterally into the CA1 region and then different doses of anisomycin (1.25-2.5 micro g/0.5 micro l) on its vehicle (saline) were injected bilaterally into the CA1 region of rats hippocampus 20 min before training each day. The results showed dose-dependent increases in latencies to find the invisible platform and traveled distances in anisomycin received group compared to the control group. Therefore, it appears that protein synthesis inhibition in the CA1 region of hippocampus impair spatial learning in Morris Water Maze.