The single dose toxicity of Buxus microphylla var koreana Nakai was evaluated in ICR mice. Twenty five mice of each sex were randomly assigned to five groups of 5 mice each and were administered singly by gavage at dose of 0, 222, 667, 2,000 and 5,000 mg/kg body weight. After single administration, signs of toxicity were observed every hour for the first 6 hours and every day for 14 days. At the end of 14-day observation period, all animals were sacrificed for gross postmortem examinations. Neither significant toxic signs nor death was observed during the observation period. In addition, no pathological changes were noticed in macroscopic examination at necropsy. These results indicate that the single oral administration of Buxus microphylla var. Koreana Nakai did not cause any toxic effect at the dose of 5,000 mg/kg body weight for both sexes and $LD_{50}$ of Buxus microphylla var. koreana Nakai is greater than 5,000 mg/kg body weight.