Carbon oxysulfide (COS) is a compound poisonous to PEM fuel cells, and it can be generated in fuel processing unit, i.e. reformer, water gas shift, and desulfurization unit. The outlet concentrations COS from packed beds made of different ZnO oxide based sorbents were measured in the breakthrough test at room temperature, 200 °C and 400 °C. The challenge gases were 1.4 vol. % H2S-32 vol. % CO-66.6 vol. % H2, and 1.4 vol. % H2S-32 vol. % CO2-66.6 vol. % H2. At room temperature, 9 different metal doped ZnO based sorbents were test for sulfur capacity. No COS was detected in the all the tests with different challenge gases; and the copper doped (1 wt. % Cu) ZnO sorbents (Cu-ZnO) demonstrated highest capacity (0.21 g Sulfur/ g of Sorbent) among all the ZnO based sorbents. At 200 °C, no detectible COS was generated in the CO2 test for both pure ZnO and Cu-ZnO sorbents; in the CO testes, Cu-ZnO did not generate any detectable COS throughout the breakthrough test, while the highest COS concentration of 200 ppmv was generated in packed bed of pure ZnO at the same test conditions. At 400 °C, COS was detected in all the tests. In the experiments of CO effect, the Cu-ZnO showed lower COS concentration than the pure ZnO sorbents, and COS concentration decreased gradually in testes for ZnO and Cu-ZnO. However, in the experiments of CO2 effect, the outlet concentration of COS in the test for Cu-ZnO increased dramatically to the equilibrium concentration of 4200 ppmv, while in the test for pure ZnO, the COS approached the equilibrium slowly. The comparative study suggests that the sorbents with high heterogeneous contacting efficiency, such as Cu-ZnO, are able to remove more sulfur without COS formation at low temperature range, namely fuel processor startup.