Adsorption of sulfur dioxide (SO2) on intrinsic and modified graphene, including Stone-Wales (SW) defect, Al doping and a combination of these two, was theoretically studied using first-principles approach based on density functional theory (DFT). The most stable adsorption geometry, adsorption energy, magnetic moment, charge transfer and density of states of these systems are thoroughly discussed. It was found that SO2 molecule is weakly adsorbed on the intrinsic and SW defected graphenes and their electronic properties were slightly changed. The Al-doped graphene and the defect-dopant combination show high reactivity toward SO2. Compared with Al-doped adsorption system, the adsorption energy for Al-doped SW defect adsorption system can be enhanced by the introduction of a SW defect. This work reveals that the sensitivity of graphene-based chemical gas sensors for SO2 can be drastically improved by introducing dopant and defect, and the Al-doped SW graphene is more suitable for SO2 gas detection. (C) 2014 Elsevier B.V. All rights reserved.