Abstract: Available molybdenum(Ⅵ) in soil sample was extracted by shaking with a mixed solution of (NH4)2C2O4 and H2C2O4 (pH 3.3). The suspended solution was filtered on a dry filter paper and an aliquot of the filtrate was evaporated to near dryness after addition of 10 g·L-1 KMnO4 acidic solution. 0.25 mol·L-1 NaOH solution was added for co-precipitation and an aliquot of the supernatant was taken and acidified with H2SO4(1+1). A mixed base solution (containing diphenyl-glycollic acid, diphenylguanidine and sodium chlorate) together with tiron solution, acting as reagents for the catalytic reaction with Mo(Ⅵ), was added, and the polarographic determination of Mo(Ⅵ) was made with the JP-303 polarograph. Values of peak current at the peak potential of -220 mV were found to keep linear relationship with mass concentration of Mo(Ⅵ) in the range of 0.8-20 μg·L-1. Detection limit (3s/k) of the method found was 0.002 6 μg·g-1. The proposed method was used in the determination of molybdenum in 5 CRM′s of soil, giving results in consistency with the certified values.