The delayed and irregular germination of Quercus seeds can negatively influence seedling quality and growth. The might be explained by several factores, including mechanical strength of the pericarp, secondary metabolites (e.g. tannins and polyphenols), plant hormones especially abscisic acid (ABA) and indoleacetic acid (IAA), and germination inhibitors. These chemicals produced in plants can prevent the seed germination of themselves or other species. The inhibitory substances in aqueous extracts of pericarp tissue which increased with acorn development have been found by Blanche. Moreover, the presence of inhibitory substances has also been confirmed in the pericarp of mature Quercus nigra acorns. However, the study on whether the germination inhibitors contained in different parts of oak acorns is still lacking. Acorns were divided into three parts: pericarp, cotyledon (cutting off 2/3 of the distal end of acorns) and embryo (here including embryo and 1/3 cotyledon around it). Then they were oven-dried (30°C), crushed and passed through 1-mm sieve. Subsequently, they were extracted in 80% methanol extracts and vacuum concentrated to 1 g/mL, some of which were diluted to 0.5 g/mL. In order to verify if the inhibitory substance in different parts of acorns can lead to delayed and uneven germination, germination percentage and root and shoot length of Beassica pekinensis seeds were investigated which cultivated in a Sanyo growth cabinet and watered by distilled water, 80% methanol extracts and the extraction phase of methanol, of petroleum ether, of aether, of ethyl acetate, and of water from the acorn embryo, cotyledon and pericarp with concentrations of 1.0g and 0.5g dry acorn weight per ml methanol (g/mL). The results showed that (1) the germination percentage, shoot and root length of B. pekinensis seeds watered by 1.0 g/mL methanol extracts from embryo, cotyledon and pericarp of Q. variabilis, Q. aliena var.acuteserrata, Q.mongolica, Q.palustris and Q. acutissima seeds were significantly lower than those from control, and the inhibitory effect of germination rates gradually decreased, and 0.5 g/mL methanol extracts from embryo, cotyledon of Q. variabilis acorns reduced the germination percentage of B. pekinensis seeds, while no significant difference was detected in germination percentage of B. pekinensis seeds between those from pericarp of all tree species acorns and the control; (2) methanol extracts from embryo, cotyledon and pericarp of Q.robur and Q. ×fangshanensis remarkably reduced shoot and root length of B. pekinensis seeds, but little response in germination percentage; (3) the inhibitory effect of Methanol extracts from embryo, cotyledon and pericarp declined in turn, with higher concentration of methanol extract having stronger inhibitory intension for each section of seeds; (4) the inhibitory strengthen of extraction phase of methanol among 5 extraction phases, was larger than that of extraction phase of ethyl acetate, resulting in the lowest germination rate, shoot or root length of B. pekinensis seeds, meanwhile,negative effects was observed in other extraction phases. The fact of extracted substances having stronger inhibitiory effect on the length of root and shoot than on the germination percentage of B. pekinensis, indicating that the inhibitors of oak seeds mainly restrict germination of root and shoot themselves, which could be the cause of the irregular germination.