Making alloys of Mg and Li is quite a task as their individual melting temperatures are vastly different. However, it is thought paid off considering their extreme lightness. Basically, low melting temperature Li could cause Mg-Li alloys' microstructures change at room temperature (R.T.). Recrystallization and aging of Li-rich solid solution phase (ß) can proceed under R.T. Previously. R.T. aging phenomenon was mentioned without in-depth analysis. This paper fills up the blank by working on Mg-11.2%Li-0.95%Al-0.439cZn (mass%). mainly due to the TEM work brought in. With this apparatus for analysis, a transition precipitate (tentatively called pre-θ phase) is revealed. This pre-θ precipitation is responsible for the distinctive strengthening in the initial stage of R.T. aging. However, it is unstable and subsequently transforms to θ or α phase. Both of these later precipitates are little effective in producing aging strengthening.