Surface functionalization of graphene oxide (GO) by grafting polymer chains to its surface is achieved by direct use of GO as the initiator for polymerization of N-vinylpyrrolidone (NVP). The functionalized GO can be readily dispersed in a variety of solvents which facilitates graphene processing for a wide range of applications. Fourier-transform infrared, X-ray powder diffraction and transmission electron microscopy investigations show that poly(vinylpyrrolidone) is grafted onto the GO surface, and X-ray photoelectron spectroscopy, elemental analysis and conductivity measurements suggest modest reduction of the functionalized GO during the surface-initialized polymerization. Both electron spin resonance and ¹³C-NMR spectra indicate that breakage of weak bonds at the defects on the GO surface initialized the radical polymerization of NVP.