WebQuest is an advanced tool which could provide the significant scaffolding to support instructors through incorpo-rating leing objects within systematic designs of leing activities. The focus of this article is to explore how a Webquest is designed reasonably and what rationales are implied in such a design through a case study of Webquest design for a group of ESL/EFL leers in Grade 12. The result indicates that a Webquest which is guided by the principles of constructivist problem solving, social interaction and scaffolding leing can be regarded as a desirable Webquest.