Abstract: The present experiment was conducted to determine the changes of hepatic and renal metallothionein mRNAs expression in response to different levels of zinc supplementation in ISA laying hens . The laying hens were divided into the groups of control, treatment 1 (60 mg/kg ) and treatment 2 (180 mg/kg) at 18 weeks of age and sacrificed after 10 weeks for tissue sampling. The levels of mRNA expression were quantified with RT-PCR, using β-actin as an internal standard. The results showed that zinc supplementation at 60 mg/kg, but not 180 mg/kg, significantly increased the hepatic MT mRNA level compared with the control (P<0.05). Additionally, the level of renal MT mRNA expression was significantly higher in 60 mg/kg compared with that in 180 mg/kg group (P<0.05), although no significant differences were observed between control and either of the two treatment groups. The results suggest that lower level of zinc supplementation significantly upregulate MT gene expression in the liver and kidney of the laying hens.