A seat sliding device including a stationary rail secured at both ends thereof to a vehicle floor through brackets, a movable rail slidably engaged with the stationary rail and mounting thereon a seat, and a protective cover for covering the bracket and said stationary rail. The protective cover comprises a bracket cover portion covering the bracket, a rail cover portion connected to the bracket cover portion and covering an end portion of the stationary rail, and means for defining a guide groove which provides a space through which the movable rail passes. The protective cover contributes to an improvement in interior appearance and safety of a passenger compartment of vehicles.