We succeeded in extracting intense O- ion beam by applying dc voltage to a microporous crystal 12CaO . 7Al(2)O(3) (C12A7) engineered to incorporate extremely large amounts of O- (1.3 x 10(20) cm(-3)) and O-2(-) (2.7 x 10(20) cm(-3)) in crystallographic cages. The O- ion beam is monochromatic and the current density (similar to2 muA/cm(2)) is higher by three orders of magnitude than the maximum value recorded for yttrium-stabilized ZrO2 (YSZ). A surface metal electrode, essential for the YSZ to dissociate a drifted O2- in the bulk into an O- and an electron on the surface, is not needed for the C12A7. The presence of extremely large concentrations of O- and O-2(-) ions and fast oxygen-ion-conductive nature of C12A7 allow extraction of O- ions directly from the surface. (C) 2002 The Electrochemical Society.