In the post-genomic era, technology development for large-scale protein analysis looms large. Recently, the significant accomplishments of genomics, proteomics and bioinformatics are making the systematic analysis of all expressed cellular components a reality. The proteome is defined as the set of all the expressed proteins in a cell, tissue or organism in a determined moment. Crotoxin is the main component from the venom of Crotalus durissus terrificus. It is a complex composed by two subunits (A e B). Subunit B is the toxic component, which has a phopholipase A2 enzimatic activity. As for subunit A, it is both non-toxic and does not have ezimatic activity. Crotoxin exerts its pathophysiological action by blocking neuromuscular transmission; its effect are primarily presynaptic, causing a typical triphasic modification in neurotransmitter release from nerve terminals (depression, facilitation, and final blockade). By preventing its nonspecific adsorption, component A enhances the blocking action of component B on neuromuscular transmission and therefore its toxicity. The phospholipase A₂ produces mithocondrial swelling and O₂ consumption. Crotoxin, in association with cardiotoxin, (VRCTC-310), has shown antitumoral activity. Although there is considerable information about effects of crotoxin, the precise mechanism of action of this molecule is not known. The objective of this study is to characterize protein expression profile induced by crotoxin in rat cerebral cortex synaptosome, using a proteomic approach. We applied a proteomic approach (bidimensional electrophoresis and MALDI-TOF-TOF mass spectrometry) to search for differentially expressed proteins between synaptosomes treated with crotoxin and control (non-treated). By analyzing total proteins separated in a non-linear pH range (3-10), using software PDQuest^TM (Bio-Rad), we detected 42 differentially expressed proteins.  From those spots a total of proteins eight spots were successfully identified by mass spectrometry: creatine kinase, actin beta, rCRMP-1, Gapd , H⁺ transporting, Vdac 1, ATP sintase and pyruvate kinase. These proteins are involved with mithocondrial swelling (Vdac 1), energetic metabolism (creatine cinase, Gapd, H⁺ transporting, ATP sintase and pyruvate kinase ) and cellular injury repair (rCRMP-1, actin beta). These results may correlate with crotoxin action described in literature.