Abstract: A method for the determination of trace arsenic in high purity cobalt with hydride generation-ICP-MS was reported. Due to the interference of the oxide complex ions ⁵⁹Co¹⁶O^＋, the background concentration of ⁷⁵As is about 100 µg•L^－1 in 1 g•L^－1 cobalt solution, which lead to the impossibility of the direct analysis for the trace As in high purity cobalt. However, the As background concentration can be decreased to several µg•L^－1 if the simple HG system was applied and the 0.05 µg•g^－1 of determination limits can obtained with this method.