In this study, a simple fluorescent sensor 2-hydroxybenzcarbaldehyde-(2-methylquinoline-4-formyl) hydrazone (HL) has been designed, synthesized and characterized by ¹H-NMR, IR, ESI-MS. Upon addition of Al³⁺, HL shows a large fluorescence enhancement (220-fold) at 484 nm. The reasons for this phenomenon are attributed to formation of a 1 : 1 complex (K_a = 5.6 × 10⁴), which inhibits the excited-state intramolecular proton transfer (ESIPT) process and photo-induced electron transfer (PET) process. Other metal ions including Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cr³⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Pb²⁺ and Zn²⁺, have almost no influence on the fluorescence. The lowest detection limit for Al³⁺ is calculated to be 7.2 × 10⁻⁷ M in ethanol.