In this work, a novel zirconium-based metal-organic framework (MOF) composite material, UiO-(OH)@RhB, has been solvothermally prepared with zirconyl chloride octahydrate, 2,5-dihydroxyterephthalic acid, and rhodamine B (RhB) for ratiometric fluorescence sensing of Al ions in an aqueous medium. The luminescence measurement results showed that, at the single excitation wavelength of 420 nm, the fluorescence intensity of the ligand at 500 nm increased significantly in the case of Al, while that of RhB at 583 nm changed slightly, together with an apparent color change. Under optimal conditions, UiO-(OH)@RhB exhibited an extraordinary sensitivity (10 nM), good selectivity, and a fast response (2 min) for Al. As far as we know, the limit of detection is superior to that of the current reported MOF-based Al fluorescence sensors. The response mechanism suggested that -OH could capture Al in water through coordination and high electrostatic affinity and achieved turn-on ratiometric fluorescence through the excited-state intramolecular proton transfer process and stable fluorescence of RhB. In addition, this sensor was also applied to actual food samples (grain beans), with the recoveries ranging from 89.08% to 113.61%. Such a turn-on ratiometric fluorescence sensor will provide a constructive strategy for the ultrasensitive detection of Al in practical applications.