Miller Fisher syndrome‐associated anti‐GQ1b ganglioside antibodies produce an acute complement‐dependent neuroexocytic effect at the mouse neuromuscular junction (NMJ) that closely resembles the effect of α‐latrotoxin (LTx). This pathophysiological effect is accompanied by morphological disruption of the nerve terminal involving the loss of major cytoskeletal components, including neurofilament. Both LTx and the membrane attack complex of complement form membrane pores that allow free ionic movement and we have previously hypothesized that Ca²⁺ ingress and the subsequent activation of Ca²⁺‐dependent proteases, calpains, may lead to substrate degradation resulting in structural disorganization of the terminal. Here, we treated mouse NMJs in hemidiaphragm preparations with anti‐GQ1b antibodies and complement, or with LTx in the presence and absence of extracellular Ca²⁺, and studied possible neuroprotective effects of the calpain inhibitors calpeptin and calpain inhibitor V. Both Ca²⁺ depletion and calpain inhibition protected the cytoskeleton from degradation, as assessed by immunohistological and ultrastructural analysis. Calpain inhibitors may therefore be useful therapeutically in limiting nerve terminal and axonal injury in autoimmune peripheral neuropathy and in human latrodectism.