Chromatographic studies (CC, VLC, MPLC, and PTLC) on ethyl acetate extract from the leaves of Quercus aucheri yielded 2 flavonoids (quercetin 3-O-alpha-L-arabinopyranoside (1), quercetin 3-O-beta-D-galactopyranoside (2)) and 2 tannin precursors and a procyanidin [(isolated as peracetates of (+)-catechin (3a), (+)-gallocatechin (4a) and epicatechin-(4 beta -> 8)-catechin (5a))]. The structures of the compounds were elucidated by UV, 1D-NMR (H-1, C-13, TOCSY) and 2D-NAIR (COSY; HSQC: HMBC) techniques. Different extracts (80% MeOH, EtOAc, n-BuOH and H2O) from the leaves of Q. aucheri were investigated for their antimicrobial activity against 2 Gram-positive and 2 Gram-negative bacteria and 3 yeast-like fungi by a broth microdilution method. EtOAc extract, which showed the highest antimicrobial activity, was further used for isolation.