Molasses and starch were used to estimate the effect of co-substrate on anaerobic slurry phase bioremediation of TNT (2,4,6-trinitrotoluene)-contaminated soil. Degradation efficiency of TNT in molasses and starch addition was approximately 97% and 87%, which is 50-60% higher than 38% without co-substrate addition. Molasses and starch addition enhanced TNT degradation. It was proved that the TNT degradation was a mainly biological process from the result of an abiotic control experiment. In case of molasses addition, overall first order degradation rate was 0.0161/day indicating the most active TNT degradation. The first order degradation rates (k1=0.0056 for molasses, k1=0.0033/day for starch) before 60 days were slower than those thereafter (k2=0.0237 for molasses, k2=0.0136/day for starch). Lower degradation rate in early stage might be due to adaptation of native soil microorganisms.