Learning induces dynamic changes to the actin cytoskeleton that are required to support memory formation. However, the molecular mechanisms that mediate filamentous actin (F-actin) dynamics during learning and memory are poorly understood. Myosin II motors are highly expressed in actin-rich growth structures including dendritic spines, and we have recently shown that these molecular machines mobilize F-actin in response to synaptic stimulation and learning in the hippocampus. In this study, we report that Myosin II motors in the rat lateral amygdala (LA) are essential for fear memory formation. Pretraining infusions of the Myosin II inhibitor, blebbistatin (blebb), disrupted long term memory, while short term memory was unaffected. Interestingly, both post-training and pretesting infusions had no effect on memory formation, indicating that Myosin II motors operate during or shortly after learning to promote memory consolidation. These data support the idea that Myosin II motor-force generation is a general mechanism that supports memory consolidation in the mammalian CNS. © 2012 Cold Spring Harbor Laboratory Press.