Web usage mining has been used effectively as an approach to automatic personalization and as a way to overcome deficiencies of traditional approaches such as collaborative filtering. Clustering is one of the important functions in web usage mining. The likelihood of bad or incomplete web usage data is higher than the conventional applications. Clustering is a process of forming groups (clusters) of similar objects from a given set of inputs. Good clusters have the characteristic that objects belonging to the same cluster are \"Similar\" to each other, while objects from two different clusters are \"Dissimilar\".