A new type of gold nanoparticles was synthesized by using benzoyl pyrazolone as a capping agent. The synthesized AuNPs exhibited a spherical shape and a monodisperse and fluorescence emission characteristic peak at 650 nm. The AuNPs –BMPBP was demonstrated as sensitive and selective fluorescent chemosensor for detection of Al 3+ ion. In the presence of Al 3+ ion, the fluorescent emission of BMPBP-AuNPs at 650 nm, increased with an increasing concentration of Al 3+ ion with a low detection limit (2 µM), the proposed method provided to apply determination of Al 3+ ion of tap water with satisfactory results.