A rib locating method on chest direct radiography (DR) image using watershed algorithm and correlation matching is presented in this paper. Firstly, the body and spine are located by employing watershed algorithm; second, the body model is selected to remove other bones outside body; thirdly, the models of left and right ribs are resized and rotated to fit ribs of each side respectively; finally, the rib regions are extracted, each one of which contains only one rib. 70 DR images are used to test the method. The experiment result shows that the average error rate, accuracy, and sensitivity are respectively 0.067, 0.828 and 0.862.