Although allowing organizations to build loosely coupled, distributed heterogeneous enterprise application, ServiceOriented Architecture (SOA) doesn’t support direct data access or manipulation to heterogeneous data sources. To lower the dependency of data access on applications, a preliminary research is conducted on data access mechanism adopting data service in SOA. Based on the analysis of applying traditional data access methods to heterogeneous data sources in SOA, data service is researched and a data access method using data service is proposed, aiming at providing direct access to data sources using web services. ADO.NET Data Service from Microsoft is employed to implement data service and examples are illustrated, proving that data service not only provides direct access to data sources, but also can be integrated into SOA through standard web service interfaces. As is shown by the comparison with other data access methods, data service offers uniformed access to heterogeneous data sources without involvement of individual applications.