--- - |2 Abstract This study examined the effect on positive and negative emotions in Japanese college students of mentally subtracting grateful events. Participants (N = 62) were randomly assigned to one of the following three conditions: (a) writing with surprise the ways that a positive thing or event might never have happened or might never have been part of life (the mentally subtracting a present good [MS] group), (b) writing without surprise the ways in which a positive thing or event happened easily or was certain to become a part of life (the counting gratitude group), and (c) no writing control. The results of analysis of variance showed that the MS group experienced significantly increased positive emotion and decreased negative emotion between pre‐test and post‐test. Furthermore, the MS group showed significantly greater positive emotion than the control group at post‐test. Surprise mediated the effects of the MS group intervention on positive emotion but not on negative emotion. Issues related to gratitude induction and mediation of surprise are discussed. - Japanese Psychological Research, EarlyView.