The Qionglai kiln site is a famous kiln site in Sichuan province, China, of the Tang dynasty (618-907 A.D.). The wares from Qionglai kiln site bear a unique national style and striking local features. A series of opaque green-glazed shards with mild gloss and jade-like feel, excavated from Shifangtang kiln site were selected as test samples. The glaze and body compositions and microsctuctures of the shards were studied by means of EDXRF, FESEM, and DTEM/SAD/EDS. The study has demonstrated that the opaque green glazes from Qionglai kiln site are high-temperature calcia-magnesia-silicate glazes and that typical phase-separated glazes of the droplet structure. The isolated droplets are rich in SiO2 and the matrix is rich in oxides of Ca, Mg, P, Ti and Fe. We have shown that Al2O3 suppresses phase separation. The droplet diameter falls in the range of 0.1~0.4 _m, causing intensive light scattering, and resulting in good opacification and jade-like texture. The green glaze from Qionglai kiln site is one of the earliest phase-separated opaque glazes in China. The study also shows that there is a close relationship of compositions between Qionglai kiln and Changsha kiln.