Abstract: Abstract This paper proposes a medical image segmentation algorithm based on object detection. With the help of an object detection network, the precise locations of the object of interest (usually an organ or diseased tissue) in medical images are obtained. And the medical images are cropped according to locations obtained by the object detection network to gain the image patches of objects of interest. By taking the key center area of the image patch of objects of interest as the examplar image and this image patch as the search image, the pixel-wise classification of this image patch is achieved by one Siamese network with the help of a pre-defined threshold. Two datasets (LITS17 and KITS19) are used to evaluate our algorithm. And experiments show that the proposed method can accurately segment organs or diseased tissues in medical images.