According to the present invention, an alphabet input device of a mobile communication comprises a keypad input including a plurality of keys for inputting alphabets; a display for displaying alphabets inputted by said keypad input; an alphabet combiner for reading the alphabet corresponding to the input of the keypad input from pre-stored database and providing the display with said alphabet from said database; and, a controller coupled to said keypad input, said display and said alphabet combiner so as to control thereof, wherein said keypad input has a 3×4 matrix which includes numeric keys distinguished by the numbers ‘0’ to ‘9’ and function keys distinguished by the characters ‘*’ and ‘#’, and said numeric keys for ‘1 ’ to ‘9’ are assigned with a plurality of alphabet buttons for inputting alphabets, wherein said numeric key for ‘0’ is assigned with a space button for inputting a blank, wherein one of said function keys for ‘*’ and ‘#’ is assigned with a last button for successive inputting of the alphabet and a special character button for inputting a special character, wherein the other of said function keys that does not assigned with said last button and said special character button is assigned with a shift button, which performs a function of character input mode-setting and word-shifting for setting a character input mode so as to allow inputting of the capital/small letter of alphabet and for shifting a word inputted beforehand between the capital letter and the small letter, and a function of character-shifting for shifting characters inputted beforehand one at a time.