This paper proposes a novel text input method based on hand gestures for wearable computers. A character is firstly written by a fingertip and then recognized through a B-splines based character recognition method. The writing procedure is controlled by hand gestures including hand tracking, gesture recognition and fingertip positioning which are performed by an extended CONDENSATION algorithm. We have integrated the proposed text input method into a wearable vision system developed in our lab and tested the resulting text input system on Graffiti 2 alphabet. The experimental result shows that our method is promising for natural text input in wearable computers.