An analytical study was made of the thermally activated motion, of perfect dislocation loops with high mobility, in terms of an elastic model; where the dislocation loops were assumed to be smooth flexible strings under the influence of a potential barrier. The activation energy and saddle point configuration of the dislocation loops were expressed analytically in the present model. The activation energy increased monotonically with loop-length and converged to a finite value. However, the features of the thermally activated motion change markedly; depending upon the loop-length. If the dislocation loops were longer than a critical length, Lc, the saddle-point configuration was of the well-known double-kink type. However, if the dislocation loops were shorter than Lc, the saddle-point configuration was the so-called rigid type. That is, the dislocation loops overcame the potential barrier without changing their shapes; except for thermal fluctuations. The former was regarded as dislocation-like transport, while the latter was termed point-defect-like migration. As the dislocation loops grew, a transition from point-defect to dislocation occurred for the dislocation loops.Activation Energy and Saddle Point Configuration of High-Mobility Dislocation Loops - a Line Tension Model. K.Ohsawa, E.Kuramoto: Physical Review B, 2005, 72[5], 054105 (7pp)