Oxide semiconductors are promising materials for spintronic applications since the performed experiments suggest of ferromagnetic ordering at room temperature. However, there are only a few papers devoted to investigation of the spin injection from the oxide-based ferromagnetic layers into conventionsl semiconductors. In order to detect the spin polarization of the injected carriers one uses as a rule light-emitting diode (LED) technique, which is especially suitable for III-V semiconductors. In this work, multilayer structure consisting of ferromagnetic Zn1-xCoxO film and diamagnetic ZnO layer has been studied. The oxide layers were grown by pulsed laser deposition and RF-diode sputtering technique. Because of limitation in using LED technique for the studied structures direct mesurements of magtnetoresistance has been applied to study the spin injection. All measurements were performed with the magnetic field directed in plane of semiconductor layers. The obtained results on magnetic field dependence of magnetoresistance in Zn0.95Co0.05O /ZnO structures show spin-valve type behavior and give clear evidence for effective polarization of the injected current.