Abstract: The aim of the study is to investigate chemical constituents of the leaves of Pieris japonica. The isolation and purification of the constituents were performed by various chromatography and spectral analysis. Three new phenolic glucosides, erythro-syringoylglycerol 4-O-β-D-glucoside (1), 1-(2-β-D-glucopyranoxyl-4-methoxyl-6-hydroxyphenyl)-3-hydroxyl-1-propanone (3), erythro-1-(4-hydroxyl-3-methoxyphenyl)-2-［4-(3-β-D-glucopyranoxypropyl)-2,6-dimethoxyphenoxy］-1,3-propanediol (4), along with five known phenolic glucosides, syringoylglycerol 8-O-β-D-glucoside (2), magnolenin C (5), syringaresinol mono-β-D-glucoside (6), 3-(4-hydroxyl-3-methyphenyl)-1-propanol-1-O-β-D-glucoside (7) and 3,5-dimethoxyl-4-hydroxybenzyl alcohol 4-O-β-D-glucoside (8) were isolated and identified from the plant leaves. Compounds 1 and 2 inhibited significantly (P<0.01) the proliferation of murine T and B cells at concentration of 1×10^-6 mol·L^-1, in vitro.