The effects of electrical charging on the electronic structure of tris(8-hydroxy-quinoline) aluminum (Alq(3)) have been studied theoretically using density functional theory, and semi-empirical and ab initio molecular orbital theories. All three methods show that negatively charged Alq(3) molecules have rather delocalized electronic structures suitable for electron transport. On the other hand, the distribution of the highest occupied molecular orbital in the Alq(3) molecule becomes highly localized upon positive charging. This localization of the frontier molecular orbital restrains movement of the residing electrons and thus inhibits the electron transport. The success of the current approach in explaining the electron transport properties of the Alq(3) molecule suggests it may be useful for the design of organic molecules for electronic applications.