The single dose toxicity of Jengjengamiyjintang, a herbal drug for duodenal ulcer was evaluated in male and female Sprague-Dawley (SD) rats. Jengjengamiyjintang was once administered to both sexes of rats at the dose levels of 2000, 1000, 500, 250 and 125mg／kg for oral route according to KFDA guidelines for single dose toxicity test (1999-61). In addition, vehicle control group was added in order to compare clinical signs, body weight changes and abnormal necropsy findings. After single administration, clinical signs were observed every twice a day for 14 days and body weights were measured 5 times including initial measurement on day 0. When observation period was over, the animals were sacrificed and macroscopic examination of major organs was conducted. Neither significant clinical signs nor death after administration was observed during the observation periods except for soft feces or diarrhea that were restricted to Day 1 of 2000 and 1000mg/kg-dosing groups. Although some accidental findings such as gross and histopathological changes of lung that were demonstrated in some animals of all experimental groups including vehicle control group, no abnormal necropsy findings and changes of body weight were observed at terminal necropsy in both sexes. From these results, it is considered that $LD_{50}$ of Jengjengamiyjintang is over 2000mg／kg in oral administration in both sexes of rats and approximated lethal dose was considered over 2000mg/kg.