Apparatus and method for inputting characters in portable terminal

A character input device of a portable terminal and a method thereof are provided to easily realize a character grouping function and a representative character designation function, and to implement excellent flexibility, thereby being applicable to various languages. A key where a representative character is marked is inputted(301-305). Characters belonging to a character set of the marked representative character are displayed(307). When a direction key is inputted, the number of the direction key is inputted is sensed(309-315). One of the displayed characters, which corresponds to the sensed result is inputted(317). Identifier of the representative character key is displayed on a central character of the displayed characters, and the central character is inputted when the representative character key is inputted.