Reactive oxygen species (ROS) are important mediators in a variety of pathological events, but the oxidative stress owing to excessive generation of ROS is implicated in many human diseases. In this work, we designed and synthesized a novel dual-functional chelating ligand, [4'-(p-aminophenoxy)methylene-2,2':6',2 ''-terpyridine-6,6 ''-diyl]bis(tnethylenenitrilo)tetrakis(acetic acid) (AMTTA), that can strongly coordinate with both Eu3+ and Tb3+ in aqueous solutions for the recognition and time-gated luminescence detection of highly ROS (hROS), hydroxyl radical ((OH)-O-center dot), and hypochlorite (ClO-). The complexes AMTTA-Ln(3+) (Ln = Eu and Tb) are almost nonluminescent because of the photoinduced electron transfer from the electron-rich aminophenyl group to the terpyridine-Ln(3+) moiety but can rapidly react with hROS to afford highly luminescent complexes (4'-hydroxymethyl-2,2':6',2 ''-terpyridine-6,6 ''-diyl)bis(methylenenitrilo)tetrakis(acetate)- Ln(3+) (HTTA-Ln(3+)). Interestingly, when the AMTTA-Eu3+/Tb3+ mixture (AMTTA/Eu3+/Tb3+ = 2/1/1) was reacted with hROS, the intensity ratio of its Tb3+ emission at 540 nm to its Eu3+ emission at 610 nm, I-540/I-610, showed a ratiometric response toward hROS, and the dose-dependent increase of the ratio displayed a double-exponential correlation to the concentration of hROS. This unique luminescence response allowed the AMTTA-Eu3+/Tb3+ mixture to be used as a ratiometric probe for the time-gated luminescence detection of hROS.