An apparatus and a method for changing a theme form of an application to conform the user experience to a web application or a native application in a portable terminal. The apparatus for changing the application theme in the portable terminal may comprise a controlling unit for changing an application theme into an application theme of a different device type, a displaying unit for outputting a change process of the application theme and the application to which the changed theme is applied, an inputting unit for generating a change request of the application theme and a theme application managing unit for converting theme data, obtained from compiled data of an application, through an inverse-compiling process, to data suitable for the theme form of a second application.