Artificial disorder was introduced gradually into monolayer graphene by controlling Ga(+) ion irradiation and the corresponding electronic transport properties regulated by gate voltage, source-drain voltage, temperature, and magnetic field were studied experimentally. An unsaturated positive magnetoresistance (MR) up to 100% at similar to 5 T was observed in as-fabricated graphene, while there is significant negative MR in disordered graphene. This phenomenon was attributed to the monocrystalline breaking and crystallite-boundary scattering in disordered graphene. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3595681]