The object of this study was to obtain acute toxicity information (single oral dose toxicity) of lyophilized water extract of Puerariae Radix (PR) in both male and female mice. In order to investigate the 50% lethal dose $(LD_{50})$, approximate lethal dosage (ALD), test substances were once orally administered to female and male ICR mice at dose levels of 2000 and 0 (control) mg/kg (body wt.) according to the recommendation of KFDA Guidelines [2005-60, 2005]. The mortality and body weight changes, clinical signs and gross observation were monitored during 14 days after dosing. Organ weight and histopathology of 12 principal organs were measured. As the results, we could not find any mortality, clinical signs, body weight changes and gross findings except for PR extracts unrelated sporadic findings. In addition, no abnormal changes related PR extracts treatment on the organ weight and histopathology of principal organs were detected except for some sporadic findings including hyperplasia of lymphoid follicles in the popliteal lymph nodes and spleen as pharmacological effects of PR extracts. The results obtained in this study suggest that the PR extracts does not cause any toxicological signs except for pharmacological effects of enhancement of Immune system. The $LD_{50}$ and ALD of PR extracts in both female and male mice were considered as over 2000 mg/kg because no mortalities were detected up to 2000mg/kg that was the highest dose recommended by KFDA and Organization for Economic Co-Operation and Development.