A novel kinetic method for determination of trace amounts of cobalt ion was proposed and validated.The method is based on adding malic acid into classical Belousov-Zhabotinskii(B-Z)oscillating chemical system to form a double substrate one.The results showed that when the concentration of cobalt ion was in the range of 5.27×10~(-8)to 5.37×10~(-12)mol L~(-1),the change of the oscillating period was directly proportional to the negative logarithm of cobalt ion concentration.The sensitivity and precision of the developed method were quite satisfactory.The limit of detection was down to 5.20×10~(-13)tool L~(-1)which was a highest sensitivity found for determination of metal ions using oscillating chemical reaction so far.Some factors influencing the determination were also examined.The method has been successfully used to determine cobalt ion in vitamin Bl2 injection. A novel kinetic method for determining trace amounts of cobalt ion was proposed and validated. The method is based on adding malic acid into classical Belousov-Zhabotinskii (BZ) oscillating chemical system to form a double substrate one. The results showed that when the concentration of cobalt ion was in the range of 5.27 × 10 ~ (-8) to 5.37 × 10 ~ (-12) mol L ~ (-1), the change of the oscillating period was directly proportional to the negative logarithm of cobalt ion concentration The sensitivity and precision of the developed method were quite satisfactory. The limit of detection was down to 5.20 × 10 ~ (-13) tool L ~ (1) which was a highest sensitivity found for determination of metal ions using oscillating chemical reaction so far. Some factors influencing the determination were also examined that the method has been successfully used to determine cobalt ion in vitamin Bl2 injection.