A liquid drop that partially wets a solid surface will slide down the plane when it is tilted beyond a critical inclination. Here we report the study of the sliding velocity of such a drop. Experiments for measuring the steady sliding velocity of different liquids of drops are performed. We then construct a scaling law that predicts the sliding velocity given the physical properties, wetting characteristics, and size of the drop. When the sliding velocity is low and the drop distortion due to inclination is small, the scaling law is shown to correctly model the functional dependency of the measured sliding velocity.