Although nanoparticles, which are comparable in size to polymer chains, are widely used as fillers to polymer matrices for developing functional and high performance materials, the dynamics of polymers constrained between solid particles has not been well elucidated. In this study, dynamics of individual polymer under such condition was investigated with fluorescent microscopy using DNA solutions as model systems. For individual T4 and lambda DNA molecules in aqueous suspensions of spherical polystyrene particles with diameter of 1 mu m, it was found that (i) the radius of gyration of DNA is independent of the particle volume fraction, phi(p) (ii) DNA diffusion is not sensitive to phi(p) up to a certain critical phi(p) where the average distance between particle surfaces is close to DNA size, and (iii) the DNA diffusion becomes slower at higher phi(p). The diffusion coefficient of DNA was larger, by a factor of 2, in the suspensions at intermediate phi(p) than in the corresponding confined geometry (channel/slit between fixed walls), whereas this difference asymptotically vanished with increasing phi(p). This result suggested that the DNA diffusion in the suspensions with intermediate phi(p) is accelerated by the particle motion. In fact, the diffusion coefficient measured for DNA in the suspensions was semiquantitatively described by the Rouse constraint-release model considering the matrix effect on the probe chain diffusion. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1103-1111, 2009