Zn0.90Co0.10O and Zn0.85[Co 0.50Fe0.50]0.15O targets were used to grow thin films by rf magnetron sputtering. XRD patterns of the films showed a strong preferred orientation along c-axis. Zn0.90Co0.10O film showed a transmittance above 75% in the visible range, while the transmittance of the Zn0.85[Co0.50Fe0.50]0.15O film was about 45%; with three absorption peaks attributed to d̃-d transitions of tetrahedrally coordinated Co2+. The band gap values for Zn0.90Co0.10O and Zn0.85[Co 0.50Fe0.50]0.15O films were 2.95 and 2.70 eV respectively, which are slightly less than ZnO bulk. The Zn 0.90Co0.10O film showed a relatively large positive magnetoresistance (MR) at the high magnetic field in the temperature range from 7 to 50 K, which reached 11.9% a 7K for the magnetoresistance. The lowest MR was found at 100 K. From M-H curve measured at room temperature shown a probable antiferromagnetic behavior, although was possible to observe little coercive field of 30 Oe and 40 Oe for Zn0.90Co0.10O and Zn 0.85[Co0.50Fe0.50]0.15O films, respectively. © 2007 Materials Research Society.