Graphene patterning and local oxidation of graphene are performed at high speed over large areas by means of controlled electrical micro-discharges, using a home-made instrument. The optimum operating voltage is determined to obtain high quality straight lines of removed graphene in a dry environment. By properly adjusting the working voltage and humidity conditions, large spots of graphene oxide are obtained with high uniformity, which paves the way to achieve large single-layer graphene oxide substrates for different applications.