Abstract: In this study, extracts of the seed coat and the decoated seeds of Paeonia ostii ‘Fengdan’ were separated by asystematic solvent separation method, and bioassay of each extractio phase was determined by the germination of cabbage seeds. Combined with gas chromatography-mass spectrometry (GC-MS), the species of endogenous inhibitors causing dormancy of P. ostii ‘Fengdan’ seeds were analyzed, and the relationship between these endogenous inhibitors and dormancy of P. ostii ‘Fengdan’ seeds was discussed. The results showed that the effects of different parts of seeds and phases on the germination of cabbage seeds were different. Extracts of the seed coat and decoated seeds in ether and methanol phases caused a significant decrease on the germination of cabbage seeds. The ethyl acetate phase of the seed coat extract demonstrated similar effects. Amongst the five phases, extracts of seed coat and decoated seed in ether phase had the strongest inhibitory effects on the germination of cabbage seeds. By GC-MS and bioassay analysis, the main germination inhibitors of seed coats may be the compounds of phenols, possibly 4,4'-methylene diphenol, phenol, pyrocatechol, 2,6-di-tert-butyl-4-methylphenol, etc. The main inhibitory substances of decoated seeds were organic acids, such as benzoic acid, oleic acid, palmitic acid, stearic acid, etc. Some amide substances may also be related to dormancy.