To provide a protective cover for a guard rail easily and rapidly post-installable on the existing guard rail and capable of effectively preventing a metal piece from additionally stuck therein by covering the head part outer peripheral portion of a fixing bolt projected to the the surface of the beam of the guard rail to close a clearance between the fixing bolt and the beam.

This protective cover for the guard rail covers the head part outer peripheral portion of the fixing bolt projected to the surface of the beam in the guard rail in which the beam is fixed to column with the fixing bolt. The protective cover is formed of a flexible sheet material capable of being laid down on the surface of the beam. A through hole in which the head part of the fixing bolt can be inserted is formed in the sheet material. The thickness of at least the peripheral edge portion of the through hole is formed thicker than the clearance between the beam and the fixing bolt.