The main purpose of the present study was to investigate the influence of interpersonal affect on causal attribution for helping and non-helping behaviors. Each subject, 168 university students in all, was randomly assigned to one cell of a 3 (positive, neutral, and negative interpersonal affect) ×2 (emergent and non-emergent situations) ×2 (sex of a potential recipient) ×2 (sex of a potential helper) design. The subject were asked to rate the likelihood of 25 different helping motives as a cause of helping behavior and the likelihood of 26 different non-helpingmotives as a cause of non-helping behavior. Major findings obtained were as follows: (1) Subjects in the positive and neutral interpersonal affect conditions attributed their helping behavior to internal, stable and general causes. They also attributed their non-helping behavior to external, unstable, uncontrollable, and specific causes. (2) Subjects in the negative interpersonal affect conditions attributed their helping behavior to external, unstable, and specific causes. They also attributed their non-helping behavior to internal, stable, controllable, and general causes. (3) The influences of the interpersonal affect on causal attribution was generally stronger than the other factors. Interaction effects between the interpersonal affect and the other factors were observed.