To prepare silica nanoparticle having biorepellent activity, the immobilization of capsaicin onto hyperbranched poly(amidoamine) (PAMAM)-grafted silica was investigated. Grafting of PAMAM onto a silica surface was achieved in a solvent-free dry system using PAMAM dendrimer synthesis methodology. The immobilization of capsaicin was achieved by the reaction of hydroxyl groups of capsaicin with isocyanate groups of Silica-PAMAM, which were introduced by the reaction of terminal amino groups of Silica-PAMAM with hexamethylene diisocyanate. The immobilization of capsaicin was confirmed by thermal decomposition GC-MS. The amount of capsaicin immobilized onto PAMAM-grafted silica was determined to be 0.10 mmol/g. Capsaicin-immobilized Silica-PAMAM (Silica-PAMAM-Cap) was dispersed uniformly in water and Tyrode solution. Stimulus activity of Silica-PAMAM-Cap was estimated using two stimulus tests, that is a magnus test and a paw licking test, to sensory nerve of mice. As the result of magnus test, it was found that the Silica-PAMAM-Cap shows stimulus activity. It was found that elution of capsaicin could be depressed by immobilizing capsaicin onto Silica-PAMAM from the result of paw licking test. In addition, the stimulus property of Silica-PAMAM-Cap to the human skin could be observed and it was found that Silica-PAMAM-Cap had acrid taste. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1800-1805, 2010