We have studied the adsorption reaction of L-Cysteine on Cu nanoparticle by S K-edge NEXAFS measurement. The Cu nanoparticle used for the adsorption reaction is fabricated by the gas evaporation method. The results of the NEXAFS measurement are given as follows. The electron transfer between Cu nanoparticle and substrate changes the chemical state of Cu nanoparticle. The behavior of adsorbed L-Cysteine is influenced by the electron transfer between Cu nanoparticle and substrate. This result suggests the possibility that the catalytic activity of nanoparticle can be controlled by the electron transfer between nanoparticle and substrate.