A portable terminal device using a touch pen and a handwriting input method thereof are provided. The handwriting input method of the portable terminal device using a touch pen includes displaying an execution screen of an application on a touch screen in response to the application being executed, overlapping a handwriting input layer, which is configured for a handwriting input, with the execution screen, inputting a handwriting image on an area of the handwriting input layer using the touch pen, determining a data type for recognizing the input handwriting image in consideration of an attribute of the area corresponding to a position in which the handwriting image has been input on the execution screen, and recognizing the input handwriting image as the determined data type, and applying a recognized result of the determined data type to the application.