The dynamics of polystyrene probe particles in poly(N-isopropylacrylamide) solutions and in gels has been investigated by dynamic light scattering. Two modes, i.e., the translational diffusion of probe particles and the cooperative diffusion of polymer chains, were successfully decomposed from CONTIN analysis. The characteristic decay time of probe particles in polymer solutions became larger by a few orders of magnitude than in water. On the other hand, in the case of polymer gels, the translational diffusion of probe particles was substantially frozen, and only the cooperative diffusion of polymer networks was observed. This probe scattering method clearly demonstrates the difference in the dynamics of polymer solutions and gels. The nonergodic nature of polymer networks is also discussed with the characteristic decay time distribution function.