Ultrasonic velocities and attenuation measurements have been carried out to characterise the fine scale precipitation events in a slow heat-treated 8090 Al–Li alloy. The alloy was subjected to a slow heating (at the rate of 10Kh −1 ) to the temperature of 463K, before and after solution annealing at 803K for 1h. The changes in bulk modulus, Young's modulus and Poisson's ratio have been obtained from the ultrasonic velocity data. The variation in hardness and density has been found to be consistent with the changes in velocities and elastic constant. The ultrasonic on-line measurements from 300 to 623K reveal clearly all the four transitions, including the formation of GP zones at 368K, formation of δ′ at 470K, dissolution of δ′ at 532K and the formation of equilibrium S′ and δ phases at 590K. The first differential of temperature dependent ultrasonic parameters is found to be particularly effective in clearly diagnosing all the fine scale precipitation/dissolution events. Differentiation between the precipitation and dissolution type reactions is also possible from careful analysis of the first differential plots.