The results of time-resolved light scattering for the phase separation of epoxy/polyethermide/anhydride blends show that the evolution of scattering vector q(m) follows a Maxwell type relaxation equation. The relaxation time may be suggested as the time taken for the diffusion of the epoxy anhydride n-mers from the PEI-rich phase by their relaxation movement, and the apparent activation energy of the relaxation movement is obtained.