Abstract: Cadmium (Cd) and mercury (Hg) are the most common pollutants found in water environment to cause tissue damages and induce apoptosis in invertebrates. To investigate the toxicological effects of Cd and Hg on the ovary of Eriocheir sinensis, the crabs were exposed to different concentrations of Cd²⁺ (0, 0.63, 1.26, 2.52, 5.04 and 10.07 mg/L) or Hg²⁺ (0, 0.06, 0.11, 0.23, 0.46 and 0.91 mg/L) for 6 days. The accumulation of Cd²⁺ and Hg²⁺ in the ovary increased significantly with the increased concentrations. The extent of oxidative stress caused by Cd²⁺ or Hg²⁺ was investigated by determining the oxidative stress indexes in the crab ovary. MDA, H₂O₂ and NO contents, MT (Metallothionein) mRNA levels and NOS activity in the ovary increased with the increased concentrations of Cd²⁺ and Hg²⁺. SOD, CAT and GPx activities initially increased, and then decreased with the increased Cd²⁺ or Hg²⁺. The result suggest that Cd²⁺ and Hg²⁺ can cause excessive accumulation of free radicals in ovary which lead to lipid peroxidation, and that MT induction in the ovary is a protective response against oxidative damage via detoxification of the ovary of E. sinensis. The induced antioxidant enzymes by Cd²⁺ and Hg²⁺ could effectively eliminate reactive oxygen species (ROS) from the tissues and maintain a redox-balance system to provide protection against Cd²⁺ and Hg²⁺-induced oxidative stress.