In order to evaluate acute toxicity of Coptidis rhizoma, 6 week- and 13 week-old male ICR mice received Coptidis rhizoma extract (600~4,800 mg/kg body weight) orally, and toxicological responses were observed for consecutive 7 days. In the mice received relatively high concentration of Coptidis rhizoma($geq$1,200mg/kg), death occurred within 3 hrs after oral administration, and its ratio in 13 week-old mice was conspicuously higher than that in 6 week-old mice. $LD_{50}$ of Coptidis rhizoma were estimated to bi 2,575 mg/kg and 1,490 mg/kg body weight in 6 week and 13 week-old mice, respectively. Coptidis rhizoma-treated animals manifested a variety of abnormal clinical findings such as ptosis, crouching, lethargy, convulsion, bizarre behavior and truning sideway. These abnormalities also ranked highly in the 13 week-old mice compared to those in the 6 week-old mice. In addition to abnormal behaviors, Coptidis rhizoma($geq$1,200 mg/Kg) significantly elevated the urinary contents of bilirubin, urobilirubin, protein and glucose, and values in 13 week-old mice was higher than those in 6 week-old animals. No toxicological response was observed at concentration less than 600 mg/kg. Our results clearly demonstrate that susceptibility of mice to Coptidis rhizoma may be related with age, indicating that younger age mice is more resistant to the Coptidis rhizoma than the older, and toxicological mechanism of Coptidis rhizoma may be closely associated with its pharmacological mechanism.