Actin polymerization is involved in key neuronal functions such as intracellular trafficking and morphogenesis. In this study, we examined the role of actin polymerization in lateral amygdala (LA) in fear conditioning memory formation. Microinfusion of cytochalasin D, an actin polymerization inhibitor, into rat LA immediately before fear conditioning training impaired the formation of long-term fear memory (LTM) but not short-term fear memory (STM). Microinfusion of cytochalasin D into rat LA immediately after fear conditioning impaired LTM. Cytochalasin D had no effect on fear conditioning memory retrieval when injected immediately before LTM test. These results show that actin cytoskeleton rearrangement is essential for fear memory consolidation.