Abstract. Approximation has been identified as a potential way of reducing the complexity of logical reasoning. Here we explore approximation for speeding up instance retrieval in a Semantic Web context. For OWL ontologies, i.e., Description Logic (DL) Knowledge Bases, it is known that reasoning is a hard problem. Especially in instance retrieval when the number of instances that need to be retrieved becomes very large. We discuss two approximation methods for retrieving instances to conjunctive queries over DL T-Boxes and the results of experiments carried out with a modified version of the Instance Store System. 1 Motivation A central issue in the Semantic Web research community is the expressivity of its underlying language and the complexity of the reasoning services it supports. There is a direct correspondence between the current Semantic Web ontology language OWL and Description Logic (DL).1 Research in DL has lead to sophisticated DL reasoners [6, 3, 5] that can be used to re...