Abstract: Spectrophotometry was used to determine Co in the waste of cobalt-molybdenum catalyst. The optimal conditions were found as following: ① maximum wavelength was 530 nm; ② mass concentration of sodium citrate solution (masking agent) was 250 g·L-1; ③ mass concentration of NaNO2 solution (oxidant) was 5 g·L-1; ④ amount of 5 g·L-1 nitroso R salt solution (toner) was 5 mL; ⑤ amount of sulfuric acid (1+1) solution was 10 mL. Linear relationship between values of absorbance and mass of Co was in the range within 0.35 mg. Detection limits (3S/N) of 10 μg·L-1 was obtained for Co. Average recovery by standard addition method was 98.9%, and RSD (n=15) was 4.6%.