Magnetic, Magnetotransport and structural properties of Cu/Co/Cu/NiFe/Femn spin-valve structures were studied before and after sequential annealing in the temperature range 240–360°C. Since no extended interdiffusion is observed, the overall deterioration of the magnetic and magnetoresistive properties of the spin valve is believed to originate from morphological and structural changes. In particular, annealing was found to decrease the magnetoresistive properties of Co as a result of structural changes within the Co layer and at the CO/Cu interface. These changes are accompanied by modifications of the magnetic properties. For annealing temperatures above 240°C, strong grain growth within the Co layer and increasing amount of fee Co explain the increased magnetic hardness of this layer.