Sensitized near-infrared fluorescence from Yb（Ⅲ）-Calcein complex in methanol solution was studied.It was found that Calcein form 2∶1 complex with Yb（Ⅲ）in a pH 8.9 buffer solution.The visible fluorescence from Calcein was quenched when complex forms,while the near-infrared fluorescence from Yb（Ⅲ） was greatly sensitized.Near-infrared fluorescence of Yb（Ⅲ）was further enhanced when second ligand,such as tributyl phosphate（TBP）,1,10-Phenanthroline（phen）and trioctyl phosphine oxide（TOPO）,was added.It was also noted that the near-infrared fluorescence from Yb（Ⅲ）could also be enhanced by addition of small amount of Er3+ ions.
