Abstract: The metallothionein (MT) is induced from synechococcus cedrorum growing in medium added gradually with cadmium chloride,and purified and characterized by means of Sephadex G-50. DEAE-cellulose (DE-52) and Sephadex G-25 colunm chromatography. The results show MT has no isoforms and is demonstrated to be homogenous by SDS-PAGE. Each molecule of MT contains 10 mercapto groups and combines with 5 cadmium atoms. Its molechlar weight is about 7.6KD,with isoelectric point being about pH4.5.Its cysteine resides account for 15.5% of all amino acid resides. The MT with a characteristic absorption maxium at 250nm is poorly stable with a large decrease of the absorption peak in low pH, and contains a little aromatic acid.