Fear conditioning is a classical behavioral paradigm used to study memory mechanisms.The actin cytoskeleton is necessary for memory formation in amygdala and hippocampus.Racl is a member of the Rho GTPases which are actin regulatory proteins and are important for many cell functions such as regulating neuronal morphogenesis.In this study, we examined the role of Racl in lateral amygdala (LA) in fear conditioning memory.Microinfusion of a specific inhibitor of Racl into mouse LA immediately before fear conditioning training impaired the formation of both short-term fear memory (STM) and long-term fear memory (LTM).The inhibitor had no effect on fear memory when injected immediately after training or before fear memory retrieval.These results show that Racl was essential for fear memory acquisition in basal amygdala.