The edge oxidation effects of chemical-vapor-deposition-grown graphene devices with nanoconstrictions of different sizes are presented. The effects of edge oxidation on the doping level of a nanoconstriction graphene device were identified by Raman spectroscopy and using the back-gate-voltage-dependent resistance. Strong p-type doping was observed as the size of nanoconstriction decreased. The Dirac point of the graphene device shifted toward positive voltage, and the positions of the G and 2D peaks in Raman spectroscopy shifted toward a higher wave number, indicating the p-type doping effect of the graphene device. p-type doping was lifted by deep-ultraviolet light illumination under a nitrogen atmosphere at room temperature. p-type doping was restored by deep-ultraviolet light illumination under an oxygen atmosphere at room temperature. Edge oxidation in the narrow structures explains the origin of the p-type doping effect widely observed in graphene nanodevices.