The dynamical behavior of a polystyrene(M-w1)/polystyrene(M-w2)/toluene ternary mixture has been investigated by Dynamic Light Scattering (DLS) and Fluorescence Recovery After Photobleaching (FRAP). The experiments were made at several total polymer concentrations C-T from dilute to semi-dilute range of concentration. In FRAP experiments, the dynamic of such a system is characterized by the existence of one relaxation mode identified to the self-diffusion coefficient D-s of the labelled polymer. This mode has been compared to the corresponding extracted D-s value from the two relaxation modes observed in DLS. The comparison between the results shows that in the semi-dilute range of concentration the agreement is good between both D-s values. As the concentration decreases, the agreement becomes less and less satisfactory, showing the limitation of the theory used to extract D-s from DLS measurements to the semi-dilute regime.