Nonlinear viscoelasticity was studied for a polystyrene solution in tricresyl phosphate; molecular weight = 5480 kg mol-1; concentration = 49 kg m-3. The longest Rouse relaxation time, τR, was estimated by fitting the Rouse theory to dynamic modulus at high frequencies. The Doi−Edwards tube model theory presumes that 2τR is the characteristic time for equilibration of chain contour length; (2τR)-1 is the rate for an extended chain to shrink back to equilibrium. The τR value was much lower than that evaluated with more widely accepted methods. However, the shear stress (σ) and the first normal stress difference (N1) in the start-up of shear flow with low rate of shear (<(2τR)-1/5) were consistent with the assumption that the contour length is always at equilibrium value. At high rate of shear (>8(2τR)-1), the maxima of σ and N1 were located at t = 2τR and 4τR, respectively, in accord with the interpretation that 2τR is the characteristic time for chain shrink. The strain-dependent relaxation modulus, G(t, γ), was also studied. At high magnitudes of shear, γ = 4 or 5, the ratio G(t, γ)/G(t, 0) decreased rapidly around t = 2τR and leveled off at t = 20(2τR): the chain shrink process plays the main role in damping but a slower process may also be involved. At γ = 1 or less, G(t, γ)/G(t, 0) decreased only at times much longer than 2τR. The damping of relaxation modulus involves some secondary process with a characteristic time longer than that of the chain contraction process.