A novel two-step UV initiated grafting method has been developed and applied on surface modification of polyamide. Anthraquinone-2-sulfonate sodium, an acid dye, was chosen as the photo-initiator. In the first step, photo-initiators were ionically bonded onto polyamide through a normal acid dye dyeing process. Vinyl monomers such as acrylic acid were then grafted onto polyamide surface in the following step. During UVA irradiation, not only monomers were grafted onto polymer surface, photo-initiator itself was also covalently bonded onto polymer. The grafted polymers were characterized by Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The degree of photo-grafting can be controlled by adjusting concentrations of photo-initiator and monomer, as well as UVA exposure time. This process demonstrated the feasibility of efficiently modifying polymer surface under low UV intensity. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 3629-3637, 2010