A Web service is defined as an autonomous unit of application logic that provides either some business functionality or information to other applications through an Internet connection. Web services are based on a set of XML standards such as simple object access protocol (SOAP), universal description discovery and integration (UDDI) and Web services description language (WSDL). Web services architectures are built on an insecure, unmonitored and shared environment, which is open to events such as security threats. Security concerns are the major barrier that prevents many business organizations from implementing or employing Web services. Based on the previous research in conflict of interest (CIR), this paper further introduces another important security concept called separation of duties (SoD) for Web services matchmaking process (WSMP). Next, this paper discusses the relationships between CIR and SoD in the context of matchmaking process. The paper then extends these two concepts into specifying and implementing CIR and SoD assertions in the newly developed WS-policy. WS-policy is an XML representation that provides a grammar for expressing Web services policies, to allow service locators to have a common interpretation of security requirements in the matchmaking process. Further, this paper presents a matchmaking algorithm for maximizing the level of SoD. Lastly, this paper also describes a prototype framework with "CIRService" and "SoDService" services for supporting CIR and SoD assertions in matchmaking process.