NBI endoscope has been shown to be a superior diagnostic tool for early stage lesion detection, equally wireless capsule endoscope has been proven a effective means of gastrointestinal tract diagnosis. In this paper, we present the first narrow band imaging wireless capsule endoscope. The dedicated dual-mode COMS sensor can offer both white light and narrow band images. Implementation results show that the designated 512- by-512 CMOS sensor consumes only 2mA at 3V power supply. The average current of the NBI capsule with a 8Mbps RF transmitter is nearly 7 mA that can work for 6 to 8 hours with two 1.5V 80mA button batteries while the frame rate is 2 fps.