This study is performed to find out the effects of selenium against cadmium toxicity. The experimental mice were divided into 6 gruops such as control group, cadmium alone treatment group, selenium treatment groups and two simultaneous treatment groups of selenium and cadmium. Mice were given intraperitoneal administration with two dosage of sodium selenite such as 1.0 mg/kg, 2.5 mg/kg body weight and cadmium chloride was administered 3.0 mg/kg body weight. After giving the challenge dose, the concentration of cadmium and metallothionein and histopathological change of liver and kidney were determined. The results were summarized as follows on 1. The simultaneously administration of selenium and cadmium significantly more decreased cadmium concentration in kidney and iiver tissues compared to the administration of cadmium only(P<0.05). 2. The simultaneously administration of selenium and cadmium more increased metallothionein concentration compared to administration of cadmium only. 3. The simultaneously administration of selenium and cadmium more decreased cadmium concentration in urine compared to the administration of cadmium only. 4. When liver and kidney tissues were observed with optical microscope, no obvious changes were visible in those tissues.