The large amount of information that is spread over the Internet is an important resource for all people but also introduces some issues that must be faced. The dynamism and the uncertainty of the Internet, along with the heterogeneity of the sources of information are the two main challenges for the today’s technologies. This paper proposes an approach based on mobile agents integrated in an information integration infrastructure. Mobile agents can significantly improve the design and the development of Internet applications thanks to their characteristics of autonomy and adaptability to open and distributed environments, such as the Internet. MOMIS (Mediator envirOnment for Multiple Information Sources) is an infrastructure for semi-automatic information integration that deals with the integration and query of multiple, heterogeneous information sources (relational, object, XML and semi-structured sources). The aim of this paper is to