Several biological databases exist which use different formats for storing data. Further, each database has its own schema and a query interface. There exist no standard conversion tools for converting data from one format to another, which makes querying multiple heterogeneous databases, a difficult task. Since XML provides a standard format for sharing and exchanging data on WWW, it is used to share information in biological databases. Various DTDs are defined for biological databases but they do not have a unified format. Same data is being represented as different formats using different DTDs. This paper provides mapping between various biological XML DTDs and ontology so that it is possible to correlate the data between the DTDs.