Abstract: King George Island consists mainly of Tertiary volcanics which contain plentiful plagioclases. In the Admiralty Bay area(including Keller Peninsula, Ullman Spur and Point Hennequin)of central Island expose predominantly basaltic andesites and andesites, and in the Maxwell Bay area (including Barton and Weaver peninsulas)of southwestern Island. Occur mainly High-A1 basalts and basaltic andesites. Chemical analyses and electron microprobe analyses indicate that plagioclases are andesine-labradorite (An41.47～61.26)for the Admiralty Bay area and mostly bytownite and anorthite. (An 72.05～ 90.97)for the Maxwell Bay area, revealing an evident chemical correlation between plagioclases and their host volcanics. In addition, plagioclases and their specific host volcanics are also corresponding in ΣREE, La/Yb and δEu. On the other and,various plagioclses have relatively similar feature of transitional metallic elements(such as Cr, Co, Ni, Zn), probably implying that contents and differentiation pattern of these elements are chiefly controlled by crystal structure rather than chemistry of plagioclase. In a word, synthetic studies show dependence of plagioclase compositions on those of their host volcanics. Considering that both the Admiralty Bay and the Maxwell Bay areas exist evolutional series from high-Al basalts to dacites, but have different mineralogy, it is suggested that high-A1 basaltic magma in the Maxwell Bay area can be the parental magma of magmatic series in the Admiratly Bay area.