Nowadays customer are confronted with plenty of choices of different brands with in a product category. But since they allocate limited cognitive capacity to different information process, they can maintain only a few numbers of brands in their memory as the shopping main set. Marketing researchers wanted to know how a brand highlight in the customers mind as a member of this limited set that come to a consumers mind for a final purchase decision. Studies in psychology indicate that personality is an important indicator in a decision process of an individual. So in this article the influence of five major personality traits on size of customers’ consideration set is studied. The product involvement also is considered as a moderating variable in this relation. The statistical population of the present study was students of University of Isfahan .The sample size has been estimated 156 and it is used RPII questionnaire and one else questionnaire for data collection.The results indicate that with in the population studied the Big Five has no significance effect on consideration set size. But cognitive dimension on product involvement has positive and direct relation with consideration set size.