The energy relaxation dynamics in Ag:Bi 2 O 3 nanocomposite films with high density of Ag nanoparticles were investigated by femtosecond pump–probe technique. For the films with relatively low Ag concentration (13.2–35.7at.%), the energy relaxation is nearly completed within 1picosecond (ps) at moderate excitation regime. For the film with 52.0at.% Ag concentration, the relaxation process consists of a fast power-dependent component (1–2ps) and a long-lived one. The different relaxation characteristics are suggested to be resulted from the differences in the structural and thermal properties of the surrounding Bi 2 O 3 matrix coupling with Ag nanoparticles.