The microwave magnetoresistance of CoFe/Cu/CoFe/FeMn spin valves and CoFe/Cu/CoFe three-layer nanostructures with high magnetoresistance has been studied. The transmission and reflection coefficients were measured at the frequency range from 26 to 38 GHz in magnetic fields up to 12 kOe. It is shown that the dependences of the transmission coefficient of spin valves are not symmetric with respect to the H = 0 axis, as well as the dependences of magnetoresistance. It is established that the relative changes in the microwave transmission coefficient are 1.5–2 times higher than the relative magnetoresistance measured at direct current. Changes in the reflection coefficient have a smaller value and the opposite sign with respect to changes in the transmission coefficient.