Instability mechanism of lamellar structures of Ti-48Al alloy solidified under high pressure was investigated. The results indicate that after 1100 ℃/12 h air cool, α₂ phase particles can hardly be seen in normal pressure solidified Ti-48Al alloy. Howerver, α₂ phase has been found in high pressure solidified Ti-48Al alloy. Incresaing the temperature to 1280 ℃, the high pressure solidified Ti-48Al alloy is easier to decomposite than normal pressure. This research has provided the basis of further studying on the microstructures and phase transformation of high pressure solidified Ti-Al intermetallics and enriched the theory of high pressure solidification.