A highly selective colorimetric chemosensor based on fluoran dye for iron cations, 2'-anilino-3'methyl-6'-dibuthylamino-N-(2'-(2 ''-hydroxybenzylideneamino)ethyl)iso-indolin-1-one-fluoran ( 5), was designed and synthesized. The chemical structures of all the intermediates and fluoran dye 5 were characterized by (1)H-NMR, (13)C-NMR, MS and elemental analysis. And its sensing behavior toward metal ions was investigated by UV-visible absorption spectroscopes. The fluoran dye 5 chemosensor showed an extreme selectivity for Fe(2+) and Fe(3+) in acetonitrile solution. Whereas other ions including Mg(2+), Pd(2+), Ni(2+), Hg(2+), Cd(2+), Ag(+), Cu(2+), Zn(2+) and Al(3+) induced basically no spectral change, which constituted a Fe(2+) highly sensitive and selective colorimetric chemosensor from colorless to black by "naked eyes." Spectral responses at lambda(max) = 653 nm reveals that dye 5 can function as OR logic gate with Fe(2+) and Fe(3+) as input variables.