We discuss the giant magnetoresistance (GMR) in magnetic superlattices with an s-d scattering model on the assumption that d states are bound in magnetic layers. The GMR is calculated by using the quantum Boltzmann equation using Kronig-Penney-type potentials. Spin-dependent interfacial scattering depends on the number of scatterers, the height of the scattering potentials and the amplitude of the wave function of the d state at interfaces, while spin-dependent bulk scattering is attributed to the spin-dependent density of states (DOS) of d states. Our model agrees well with the measured GMR in Co/Cu superlattices with artificially mixed interfaces, when we assume that the minority-spin d states are strongly bound in Co layers. Therefore, the spin-dependent scattering in Co/Cu superlattices is attributed to the spin-dependent DOS of the d states in the Co layers.