Polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) and polybrominated diphenyl ethers (PBDEs) were characterized and quantified in stack gas from secondary ventilation systems from five different steelmaking plants. The concentrations of 2,3,7,8-substituted PBDD/Fs (2,3,7,8-PBDD/Fs) and PBDEs were 0.036–0.19 ng/Nm3 (0.32–4.33 pg toxic equivalency (TEQ)/Nm3) and 3.11–40.0 ng/Nm3, respectively, in the stack gas. These concentrations were lower than those in other metallurgical processes, such as electric arc furnaces and iron ore sintering processes. The concentrations of PBDEs were 26–94 times higher than those of PBDD/Fs in the stack gas. The PBDD/F and PBDE emission factors in the stack gas from the steelmaking converter processes (per tonne of steel produced) were 0.048–0.59 µg/t (0.66–20.8 ng TEQ/t) and 6.36–76.6 µg/t, respectively. These data are helpful for establishing an emission inventory of PBDD/Fs from the converter steelmaking industry in China.