Most stereo cameras are equipped with lens modules of fixed focus to capture images. To provide sharp images over a wide range of object distances, stereo cameras with adjustable focus lens modules have been developed. Although such stereo cameras can be controlled by performing existing monocular autofocus for each individual camera independently, the lack of coordination between the stereo cameras and the underutilization of depth information embedded in the image data make the approach not as efficient as it can be. In this paper, we propose a novel stereo autofocus approach that exploits the disparity of stereo images to control lens movement. Experimental results show that the proposed approach can bring the lenses to the peak zone of the focus profile within two lens movements in most (92.3%) cases even if the lenses are initially far from the in-focus position.