The electrochemical reactions of selenium species in a basic AlCl3-NaCl melt has been studied by measuring EMF of an Na/SeCl4 cell. The reaction mechanism between elemental and tetravalent selenium consists of at least four electrochemical steps, including intermediates such as Se2+, Se-2(2+), and Se-8(2+). The reaction sequence from Se4+ to Se-8(2+) is discussed. The formal potential for each reaction is also determined.