Nowadays, many Web sites employ dynamic Web pages by accessing a back-end database and formatting the results into HTML pages. Performance is one of the issues that today?s Web-enabled applications should deal with. Throughput, network bandwidth usage and user-perceived delay are some of the performance measures. Abandonment of Web sites increases if they fail in meeting performance requirements. Caching is one of the key techniques that addresses the performance of such applications. In this paper, we focus on caching in Web portals, one of the emerging applications on the Web. Web portals provide a single interface for accessing different sources. We study a caching strategy based on the collaboration between portal and providers. Our experimental results show that the collaborative strategy out-performs the existing caching strategies.