The present invention relates to a novel dihydroxyphenyl-based stereoisomer having Hsp90-inhibiting activity and a pharmaceutical composition or health functional food comprising the same. Being observed to exhibit an Hsp90-inhibiting effect that is too great to predict from and is 30 or more times higher than a racemate thereof, the stereoisomer can find useful applications in a pharmaceutical composition for prevention or treatment of an Hsp90-mediated disease selected from the group consisting of cancerous disease, neurodegenerative disease, and viral infection or in a health functional food for prevention or alleviation of an Hsp90-mediated disease selected from the group consisting of cancerous disease, neurodegenerative disease, and viral infection.