Abstract: In order to solve the problem of segmenting the tongue body from a tongue picture, a novel algorithm is proposed, which is based on prior knowledge of color, shape and position of tongue body. Using HIS color model, our algorithm preserves the contour of tongue body while information of lip and face tissues are removed accurately. After that, the contour is refined by a regularization model of tongue body. Finally, the tongue body is extracted by an improved GAC algorithm. Experiments show that the proposed method works well in presence of lip and face tissues. In addition, good results are obtained by the proposed algorithm in spite of the sunken area and blurred contour of tongue body. Accurate segmentation of tongue body plays an important role of preparing good extraction of coating on the tongue.