Thiourea is a typical nitrification inhibitor that shows a strong inhibitory effect against the biological nitrification process. The 50% inhibitory concentration (IC50) of thiourea on nitrification was determined to be 0.088 mg g VSS-1, and nitrifiers recovered from the thiourea inhibition after it was completely degraded. The thiourea-degrading ability of the sludge system was improved to 3.06 mg gVSS-1 h-1 through cultivation of thiourea-degrading bacteria by stepwise increasing the influent thiourea concentration. The dominant thiourea-degrading bacteria strain that used thiourea as the sole carbon and nitrogen source in the sludge system was identified as Pseudomonas sp. NCIMB. The results of this study will facilitate further research of the biodegradation characteristics of thiourea and similar pollutants.