A novel strategy by means of poly diallyl dimethylammonium chloride (PDDA) was used to make highly mono-dispersed positively charged gold nanoparticles, and 5-ALA was immobilized onto the gold nanoparticles through electrostatic interaction. The conjugation of 5-aminolevulinic acid (5-ALA) and gold nanopartilces were characterized by the integrated tools of resonance Rayleigh scattering (RRS), UV-Vis absorption spectra, transmission electron microscopy (TEM) and laser light scattering. The results demonstrated that 5-ALA can be attached onto positively charged gold nanoparticles. This new photosensitizer is significant for enhancing PDT efficacy clinically.