ZnO varistor doped with ferromagnetic manganese oxide (La07Sr03MnO3) was prepared by conventional electric ceramic technique. There are secondary phases, La07Sr03MnO3 and LaMnO3, existing at the grain boundaries. The content of insulating phase of LaMnO3 obviously affects the electrical properties of the samples. The samples still remained ferromagnetism after doping. Applied magnetic filed could change the electrical property. The resistance increased when magnetic field was applied, showing a positive magnetoresistance (PMR) phenomenon. The existence of PMR is due to the broadening of barrier at the grain boundaries caused by the magnetic field.