Nitrate in agricultural drainage water has been one of the most contributing sources of nitrate contamination of surface water in China. Denitrifying bioreactors are a promising technology to reduce the amount of nitrate, in which an external carbon is necessary to maintain continuous denitrification. Corn cob, wheat straw and woodchips, amended with different amount of cow dung liquid, were mixed with soil and incubated anaerobically for 90 days. KNO₃ was added periodically to maintain NO₃-N concentrations between 50 and 200 mg/L. All the substrates stimulated NO₃-N removal, and cumulative NO₃-N removed from highest to lowest was: corn cob, wheat straw and woodchips. Substrates with cow dung liquid stimulated more NO₃-N removed than those without. Concentrations of ammonium and organic nitrogen in systems with cow dung liquid were higher than without. Corn cob and wheat straw lead to higher NO₃-N removal rates than woodchips, but these two substrates degraded more rapidly, which could not maintain long term denitrification. The addition of cow dung liquid to woodchips significantly increased NO₃-N removal rates over woodchips alone, but the rates were still much less than that of corn cob and wheat straw.