The catalytic effect of osmium on the oxidation reactions of three basic dyes: methylene blue (MB), butyl rhodamine B (BRB) and nile blue (NB), by KIO4 are investigated spectrophotometrically and applied for the kinetic determination of osmium (IV) in the acidic medium at 90±0.5℃. The above reactions are monitored spectrophotometrically by measuring the decrease in the absorbance at 660nm, 555nm and 600nm for the catalytic reactions of MB, BRB and NB, respectively. Under the optimum conditions, osmium (IV) can be determined at the concentration up to 3.2mg L-1 for MB method, 6.8mg L-1 for BRB method, and 10.0 μg L-1 for NB method with the respective detection limit of 0.020, 0.020 and 0.080μg L-1. The methods, which are of high sensitivity, good selectivity and stability, are free from most interference and have been successfully applied for the determination of trace amounts of osmium in some ore and catalyst samples. The kinetic parameters of the catalytic reaction were derived, and its mechanism was suggested.