It is difficult to provide Web services on a mobile environment because of the intermittent disconnection of a wireless network and the frequent change of context information. Research on hosting, migrating, and replicating Web services on mobile devices is still in its early stage. This paper presents an efficient method for establishing a policy of migrating Web services on a mobile environment. Based on WS-Policy, the proposed method defines a policy schema, which provides constructs for describing various kinds of contextual information including the requirements of a possible target host. Specifically, the schema is designed to be extensible enough for different service providers to use different vocabularies to describe their policies. To show the validity, the proposed method for establishing a migration policy has been applied to our mobile Web services framework, which supports migrating Web services among mobile devices.