A new type of amphiphilic chitosan derivative, deoxycholic acid-hydroxypropyl chitosan (DCA-HPCHS), has been synthesized through coupling reaction between 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride, N-hydroxysuccinimide, and deoxycholic acid which acts as hydrophobic group. Physicochemical properties of DCA-HPCHS in aqueous media were studied by surface tension and fluorescence measurement. It was also used to prepare gold nanoparticles at room temperature by green synthesis. Results showed that DCA-HPCHS can be concentrated on the surface to decrease the surface tension, and to associate with hydrophobic chains to form aggregates in the solution. With increased degree of substitution of the hydrophobic group, the surface tension decreased at the same concentration of the derivative, and the aggregates formed at lower concentration of the derivative. The form and size of the aggregates were analyzed by transmission electron microscopy and dynamic light scattering, which showed that the aggregates were spherical, and the size of them in solution increased with increasing concentration. In biosynthesis of gold nanoparticles, DCA-HPCHS acts as reducing and stabilizing agent, and the pH of DCA-HPCHS solution influenced the shape and size of the gold nanoparticles. And the results indicate that it is a potential material used in green synthesis of metal nanomaterials.