The present invention provides a water-soluble fluorescent compound of resveratrone 6-O-β-glucoside [(E)-4-(8-hydroxy-6-(((2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yl)oxy)naphthalen-2-yl)but-3-en-2-one] and its derivatives of Formula I which have at least one water-soluble substituent, and a method for preparing the same by a photochemical reaction of resveratrol 3-O-β-glucoside and its derivatives of having Formula 3 which are not fluorescent.Said new water-soluble fluorescent compounds has single-photon absorptive characteristics and/or two-photon absorptive characteristics as well as no or little toxicity, and can be usefully utilized in fields that requires water-soluble fluorescent characteristics (diagnosis, fluorescent probe, in vivo imaging, display, etc.).