Any modern organization hoping to retain a competitive advantage must be capable of integrating knowledge. Recent studies have explored various factors that may affect knowledge integration in information systems development (ISD) projects. Although diversity within an ISD team has been found to significantly reduce knowledge resource risks, it has also been found to lead to conflict which may harm team performance. We argue that similarity among team members—as opposed to diversity—affects member interaction which is the basis for effective knowledge integration. Based on similarity-attraction theory, this study investigated the effects of similarity and attraction on knowledge integration. The research framework includes three similarity factors (demographic, cognitive, and goal similarity), interpersonal attraction, and social integration for knowledge integration in ISD teams. The model was tested using a field study of 264 participants from 74 ISD project teams. The results confirmed the existence of the similarity-attraction effect. That is, similarity will affect interpersonal attraction among members which inspires social integration, eventually facilitating knowledge integration. The findings suggest that ISD managers intending to promote knowledge integration should carefully consider team composition since similarity and attraction can potentially affect knowledge integration in ISD project teams.