To provide a method for easily preparing ylidoid compounds from gardenia without being disturbed by crocin in fruit, chlorophyll in leaves or the like.

Ylidoid compounds contained in white flowers of gardenia, particularly in white flowers of a double flower species of gardenia are extracted with a solvent composed of at least one of a lower alcohol and water. For example, white flowers of gardenia are cut off, ground in a solvent composed of at least one of a lower alcohol and water and filtered, and the filtrate is condensed and purified by chromatography to obtain crude crystals of ylidoid compounds. Further, the filtrate (extract) can be used in dyeing silk cloth and the like by directly adding an amine thereto to be allowed to develop color in the presence of a β-glycosidase, and silk cloth and the like can be dyed in various colors of blue series.