The concentration dependence of characteristic time τrfor self‐diffusion coefficientDsof linear polymers in good solvents was discussed in comparison with that of the weight average relaxation time τwfor viscoelastic properties. Similarities were found for the concentration regions of τrand τw , and also for the concentration dependences of τ’s in the respective regions. On the basis of the similarities, it is pointed out that almost all theDsdata of polymers at finite concentrations so far published should not be discussed in terms of the reptation model since the solutions are not regarded as those in the well entangled regions.