The present invention relates to an apparatus and a method for providing a virtual API for a web-application mashup service. The apparatus for providing a virtual API includes: a screen data obtaining unit configured to obtain a website screen by accessing a website based on website access information or obtain an application program execution result screen by executing an application program based on application program execution information; and a virtual API processing unit configured to capture an interested area from the website screen related to a virtual API called by a client or from the application program execution result screen and provide the captured predetermined area of interest to the client.