The purpose of the present study was to explore the applicability of Weiner's attributional model of motivation to the study on helping behavior. It was predicted that willingness to help the person in need would be influenced by the attributed causes of the need and that the relationship between the attribution and helping behavior would be mediated by affective reactions to the request and expectancy of future need. Two hundreds and four subjects were asked to rate the likelihood that they would lend class notes to an acquaintance or to an intimate friend in each of eight conditions under which causality varied along three dimensions: stability, locus, and controllability. They also rated their emo-tional reactions on 8 scales and estimated the likelihood that the person would require aid again in the future. Analysis of variance revealed that both the willingness to help and affects were influenced by all three causal dimensions and the intimacy of relationship. Consistent with the mediation hypothesis, a path analysis revealed that controllability and stability of cause had great influences on negative affect, and the intention of help were influenced by affective reactions to the request. Contrary to expectation, the predicted mediational effect of expectancy of future need was not observed.