The speckle, which is due to the interference of coherent light scattered by a random surface, can severely degrades the image quality. The speckle properties are usually measured by a camera, which takes images of the center of a projection screen. As a result, the effects of different viewing angles are not considered. In this paper, the dependence of speckle contrast ratio on the viewing angles in a laser projection system is studied. Two major effects have been considered in the studies. First, different viewing angles result different projection distances. Secondly, for a rough screen, there exists an angular intensity distribution for the reflected/scattered light, which is determined by the structure of the screen surface. By combining these two effects, the experiment results show that the speckle contrast can vary significantly for different viewing angels. It is found that speckle contrast decreases with increase of viewing angle. As a result, when evaluating the speckle contrast in a laser projection system, the dependence of viewing angle should be considered.