We present a theoretical study of ethanol cation under an electric field due to the existence of laser field in order to understand the influence of electric field on the mass spectrum of ethanol. The electric field was applied to the four major reaction channels of an ethanol cation, such as the conversion between C2H5OH+ and c-C2H5OH+, CH3-elimination and two alpha-H-eliminations, respectively. The correlation between product distribution and field strength is quite complex due to the different responses of the reactants and transition states toward the external electric field. This makes the product distribution change as field strength varies. (C) 2007 Elsevier B.V. All rights reserved.