The Web service has become an essential concern for developers. Users have to select a service from a number of available services that best fit for their use. It is hard to discover the most appropriate web service from a large collection of web services. Quality of service depends upon the numbers of parameters. Every attribute of the QoS has its own effect on overall quality of service, which will change every time based on the service and user requirement. However, most of the researches in this field have concentrated on the study of each independent attribute of web service or based on their pre-defined priority of attribute. The article presents an overview of challenges that comes in order to select appropriate Web service also it give a road map for future research.