Ambiguous　decision-making　involves　different　processes.　However,　few　studies　have　focused　on　the　evaluation　process.　In　this　study,　event-related　potentials　(ERPs)　and　event-related　spectrum　perturbation　(ERSP)　techniques　were　used　to　explore　the　neural　dynamics　underlying　the　evaluation　process　of　ambiguous　options　through　an　ambiguous　choice　task.　Some　important　results　emerged.　We　found　a　preference　for　lotteries　with　low　ambiguity　regardless　of　reward　amount,　suggesting　that　subjects　were　averse　to　ambiguity　in　our　paradigm.　Our　electroencephalography　(EEG)　results　clarified　the　neural　dynamics　underlying　the　evaluation　process.　In　the　time　domain,　lotteries　with　both　a　larger　reward　and　lower　ambiguity　elicited　a　larger　P3.　In　the　time-frequency　domain,　larger　amplitudes　of　delta　activity　at　200–400　ms　and　500–600　ms　post-stimulus　were　elicited　by　lotteries　with　low　ambiguity.　Moreover,　lotteries　with　a　larger　reward　elicited　larger　amplitudes　of　delta　activity　at　400–600　ms　post-stimulus.　Our　ERPs　and　ERSP　results　suggested　that　individuals　in　our　paradigm　evaluated　ambiguity　and　reward　separately,　and　then　integrated　their　evaluation　to　form　subjective　values　of　different　lotteries.　©　2019　Zhu,　Pan,　Wang,　Li　and　Wang.