A reinforced fiber sheet for use in repairing/reinforcing concrete structures including a net-shaped fabric substrate and reinforcing fibers uni-directionally and uniformly arranged on either side or both sides thereof. Also, a reinforced fiber sheet for use in repairing/reinforcing concrete structured including a first and a second substrate and reinforcing fibers uni-directionally and uniformly interposed between the first and second substrates. The substrate is a net-shaped fabric formed by cross-arranging organic or inorganic fiber strands and impregnating them with thermoplastic resins, and the reinforcing fiber is attached and bonded to the substrate by the thermoplastic resin.