A new dyes-decolorizig bacterial strain N-4 was isolated from soil sample. It was indentified as Leucobacter sp. by 16S rDNA gene sequence analysis. The optimal conditions for the decolorization of the reactive dark blue K-R determined by response surface methodology (RSM) were as follows: 10 g/L of strains N-4, 222 mg/L of initial dye concentration, 1.5 g/L of (NH3)2SO4 and 3.5 g/L of fructose. It was shown that about 100% of 222 mg/L dye could be decolorized within 10 h under these conditions. Besides, strain N-4 could decolorize 9 kinds of dyes effectively. And K+, Ca2+, Mg2+, Ba2+, Mn2+ could improve the decolorizaion, while Ni2+, Cu2+ and Hg2+ inhibite the decolorization obviously.