Abstract: Metallothionein (MT) is a family of cysteine-rich, low molecular weight proteins. It involves heavy metal detoxification, maintain metabolic balance free radical scavenging metal elements and other physiological functions. A large number of studies show that the expression level of MT can indirectly reflect the stress response of organisms to the environment and the ability of detoxification of heavy metals. As a result, it is often used to evaluate the pollution status of heavy metals and the adaptability of organisms to these heavy metals. Therefore, MT presently has been selected as one of the biomarkers of marine environmental monitoring by the United Nations Environment Program. In this study, by using RACE technology to gain 636 bp of metallothionein (Ml-MT) gene cDNA sequences from total RNA reverse transcription product. The sequence contains 65 bp of 5' Untranslated Region (UTR) and 340 bp of 3' UTR in addition to 213 bp of the open reading frame (ORF), which can encode 76 amino acids. Of this, accounting for 27% cysteine, no aromatic amino acids and there are 16 MT of the specific Cys-Xn-Cys structure, where the molecular weight and theoretical isolectric point were predicted to be 7.704 kD and 7.138 respectively. The MT amino acid sequence alignment comparative analysis indicated that the M. lamarckii and Meterix lusoria were similar at more than 88%, with M. meretrix homology of 87%. The quantification real-time PCR (qRT-PCR) detection showed that there were MT expressions in five kinds of tissue of M. meretrix. These expressions had tissue specificity where visceral mass had the highest levels, followed by the Gill filaments, adductor muscle, mantle and foot. In Cd2+ 0.13 mg/L exposures of 0, 6h, 12h, 24h, 48h, 72h and 96h, the MT mRNA of M. meretrix visceral mass displayed different increasing degrees of contamination time. Specific performance is high-low-high-low wave trend changes. Except for 6h, the other time points compare with control group have significant difference (P0.01). This study showed that MT gene in the maintenance of normal physiological function of the body play an important role of molecular regulation in Cd2+ stress of M. meretrix.