For the first time, we have succeeded in observing the dynamics of laser-induced phase separation in a water/2-butoxyethanol mixture by applying nanosecond time-resolved light scattering on a submicron scale. The scattering revealed that the domain size of the mixture during phase separation was almost constant at 300 nm for 10 mu s after a laser T-jump, and the light scattering intensity increased exponentially with time. The results clearly indicate that the early stage of spinodal decomposition described by Cahn-Hilliard theory occurred in the mixture for 10 mu s.