Dynamics of flexible linear polymers in dilute solution under circular Couette flow was examined through dynamic light scattering measurements for two polystyrene samples (Mw=1.92×105 and 7.10×105) in benzene at 25 °C and at a fixed scattering angle, 75.6°. The scattered light from the sample solution, which solution was put into a gap between an inner rotating and an outer stationary glass cylinders of a rotating cylinder viscometer and was set under given shear flow, was measured with the homodyne method. For the lower molecular-weight sample, the obtained correlation function A(t) was of single exponential decay (the decay rate Γ1) over all the shear gradients γ measured at γ=0–5.2 s−1. For the higher molecular-weight sample, however, A(t) was of double exponential decays (the decay rates Γ1 and Γ2) at lower γ, and of single exponential (the decay rate Γ1) at higher γ. Any sigmoidal decay feature was not detected in A(t), so that the effect of the polymer convection on A(t) was excluded completely. The translational diffusion coefficient of the polymer D1 at given shear gradient was thus evaluated distinctly from Γ1. The obtained D1 increased with the increase of γ and gave the relation D1∝γ1/2. This D1–γ1/2 relation could not be explained by the hydrodynamic descriptions of polymers so far proposed theoretically for the dilute solution (the so-called macroscopic description), where the diffusion-type equation for the polymer configurational distribution function has been used with the assumptions that the polymer segments travel in a continuous viscous medium of a constant friction coefficient and that the hydrodynamic interactions can be described approximately by the Oseen tensor, a solution of a linearized Navier–Stokes equation of motion. It is suggested that the present results obtained in Couette flow, the flow being a rigorous solution of the Navier–Stokes equation, could not be explained without taking into account the microscopic descriptions for polymer dynamics, i.e., the hydrodynamic coupling between the polymer and the solvent. Moreover, the intramolecular relaxation motions were found to be suppressed by the shear flow if the shear gradient became larger than 0.8 s−1. This suppression is caused by the decrease in the amplitudes of the normal-mode type of internal relaxation motions, not by the extinction of their intrinsic internal frequencies.