The present work describes a selective, rapid and sensitive method for the determination of cobalt using the adsorptive differential pulse voltammetry technique. The method is based on the accumulation of Co(II) complex with 2-aminocyclopentene-1-dithiocarboxylic acid on a hanging mercury drop electrode, followed by measurement of the current of the adsorbed complex. The effects of experimental parameters on the peak current were investigated. The current was linear from 0.010 to 0.150 ?g/ml of Co(II), with detection limit of 1.5 ng/ml. The relative standard deviation for ten replicate analyses of 0.02 and 0.06 ?g/ml Co(II) was 2.3% and 1.2%, respectively. The method was used for the determination of Cobalt in steel sample.