A new Schiff base based on vanillin and naphthalimide was designed and synthesized as fluorescent probe. The probe showed high selectivity for Ag+ over other metal ions such as Pb2+, Na+, K+, Cd2+, Ba2+, Cr3+, Zn2+, Cu2+, Ni2+, Ca2+, Al3+ and Mg2+ in aqueous solution. A new fluorescence emission was observed at 682 nm in the presence of Ag+ ion. The fluorescence intensity quenched with increasing the concentration of Ag+ at 682 nm. The method of job's plot confirmed the 1:2 complex between Ag+ and probe, and the mechanism was proposed.Graphical abstractHighlights► The study lies in the design and synthesis of a new fluorescent probe (4DVN). ► The probe was synthesized based on vanillin and naphthalimide. ► The probe showed high selectivity for Ag+ over other metal ions in aqueous solution. ► The probe was sensitivity to high pH.