The formation and growth of δ′ particles in an alloy of A1-7.87at% Li have been investigated using the small anglex-ray scattering technique. It has been shown that a transition zone, which exists between the δ′ phase and the matrixafter ageing for 16 h, disappears after ageing for 32 h. The existence of a transition zone indicates that the δ′ phase isprecipitated in the procesof spinodal decomposition. This result also indicates that the growth of δ′ particles shouldbe divided into two stages. /During the first stage, the δ′ phase increases eating up the transition zone before ageing for32 h, and in the second stage it grows by swallowing up each other after ageing for 32 h. In the latter stage, the largerand smaller δ′ particles can coexist in the alloy.