Abstract: Thiourea(TU) chitosan(CTS)-Ag+ complex was prepared by the reaction of thiourea chitosan with a trace amount of silver ion in homogeneous solution, and was characterized by FT-IR. Antimicrobial activities of CTS, TU-CTS, TU-CTS-Ag+ complex and AgNO3 were evaluated against E.coli and S.aureus in vitro, and the minimum inhibition concentration(MIC) and the minimum bactericidal concentration(MBC) were determined. The results show that the complex has stronger antimicrobial activities than chitosan and thiourea chitosan. The MIC and MBC of thiourea chitosan Ag+ complex are both 100 mg/L(free silver ion content 0.032 mg/L), lower than the MIC and MBC for AgNO3, which are both 120 g/L.

Key words: chitosan, thiourea chitosan, antimicrobial activity, trace amounts of silver iron