Abstract: A hay bale cover for use with large cylindrical hay bales stored outdoors for protecting such bales from inclement weather such as rain, snow, hail and the like. The cover is in the form of an arcuate panel of flexible resilient material having a plurality of longitudinally extending, parallel ribs formed therein which extend from end to end of the panel to provide longitudinal rigidity but enabling the side edges of the panel to be flexed to vary the radius of curvature of the panel. The end edges of the panel each have an inwardly extending flange with radial corrugations therein. This enables the cover to be positioned on top of a cylindrical hay bale which is positioned horizontally on the ground surface or the like and forced downwardly thereon so that the side edges are capable of flexing outwardly and the inherent spring-like action will then cause the cover to snugly fit and actually cling to the hay bale, thereby eliminating the necessity of using tie-downs.