Objectives : This study was carried out to evaluate the acute oral toxicity of Alismatis Rhizoma in Sprague-Dawley(SD) rats. Methods : male and female rats were administered orally with Alismatis Rhizoma water extract of 1,000 mg/kg (low dosage group), 2,000 mg/kg(middle dosage group) and 4,000 mg/kg(high dosage group). We daily observed number of deaths, clinical signs and gross findings for 7 days. After 7 days, we measured body and organs weight. Also we analyzed hematological changes. Results : No dead SD rats and no clinical signs were found during the experiment period. Also other specific changes were not found between control and treated groups in hematology and serum biochemistry. In addition no significant changes of gross body and individual organs weight. Conclusions : These results suggest that water soluble extract of Alismatis Rhizoma has not acute oral toxicity and oral $LD_{50}$ value was over 4,000 mg/kg in SD rats.