A noise reducing cover for use with an internal combustion engine, taking the form of a cylinder head cover, an oil pan, a valley cover, a valve lifter cover or the like, is constructed of a main body portion of a resilient porous material, and an inner skin layer of a resilient non-porous material, securely connected to the inside of the main body portion. The noise reducing cover excludes a hard layer made of metal or hard plastic, thereby suppressing vibration of the noise reducing cover itself even when engine vibration is transmitted thereto.