The invention concerns a novel method for preparing tetrakis(pentafluorophenyl)borate derivatives of general formula MB(C6F5)4, M being selected among Na+, Li+, or K+, wherein: (a) a C6F5X solution, X being selected among H, Cl, Br or I, in anhydrous butylic ether is contacted with an alkyllithium, the mol ratio of C6F5X/alkyllithium being 1 to 1.1, and the alkyl radical, linear or branched comprising 1 to 10 carbon atoms; (b) the resulting product is contacted with previously non-dissolved BR3, R, identical or different being selected among a chlorine atom, a fluorine atom, a bromine atom, an alkoxy radical comprising between 1 and 4 carbon atoms.