The present invention provides a method for preparing a glycoside of a flavonoid compound, which comprises the step of treating flavonoid and a glycosyl donor with an enzymatic agent having glycosylation activity and being derived from the genus Trichoderma (preferably Trichoderma viride or Trichoderma reesei). Such a flavonoid compound includes a catechin compound or a methylated derivative thereof, and the glycosyl donor includes a carbohydrate containing a maltotriose residue (preferably maltotriose, maltotetraose, maltopentaose, maltohexaose, maltoheptaose, dextrin, γ-cyclodextrin or soluble starch). Glycosides obtained by the present invention have higher water solubility, improved taste, and increased stability. The present invention also provides novel glycosides of catechin compounds, which are obtained by the method of the present invention.