Along with the economic development and the society progress, knowledge service is more and more popular and gaines much more attention than ever by users.The paper points out the connotation and features of knowledge service, analyzes the necessity of carrying out information service in hospital libraries and existing problems in realizing process, as well as the measures that should be taken. Then it clarifies that from the information service to knowledge service is a strategy choice for library future development, also a new challenge to hospital libraries.