Abstract: Based on the catalytic action of Mo(Ⅵ) on the oxidation of KI by H2O2 in dilute H3PO4 medium to give free iodine (in form of I-3) which in turn reacted with acridine orange leading to quenching of fluorescence of acridine orange,a fluorophotometric method for determination of Mo(Ⅵ) was proposed.Linear relationship was found between values of ΔF(F0-F) determined at wavelengths of 446 nm (λex) and 505 nm (λem) and concentration of Mo(Ⅵ) in the range of 0.16-2.4 μg·L-1.Limit of detection (3s/k) of the method found was 0.10 μg·L-1.The proposed method was used in the determination of Mo(Ⅵ) in samples of green bean,tea and mineral water,giving values of recovery ranged from 93%-99%,and of RSD′s (n=5) less than 5%.