A new rhodamine B derivative (RDBSF) sensor was synthesized and characterized. Studies show that RDBSF exhibits high sensitivity and selectivity toward Fe3+ in Tris-HCl (1 mM, pH 7.4) /30% MeCN. The binding association constant (Ka) of RDBSF for Fe3+ was estimated as 1.52 × 104 M-1. The detection limit of Fe3+ by RDBSF was further determined as 11.6 nM. RDBSF can be used as a fluorescent probe for the detection of Fe3+ in HepG-2 cells.