Objectives: Ephedrae herba, also known as Ma-huang, is a traditional Korean medicinal herb. It has been used to treat asthma, nose and lung congestion, and fever with anhidrosis for centuries. Recently, Ma-huang was used as a source of ephedrine in many dietary supplements for weight reduction in the United States. The objective of this study was to investigate the subacute toxicity of ephedrae herba extract in rats. Methods: SPF Sprague-Dawley male rats were administered orally with ephedrae herba extract for 4 weeks as several doses(0, 125, 250, 500, 1,000, and 2,000 mg/kg). We examined number of deaths, clinical signs, body weights and gross findings for experimental period. Results: No dead animals were found during the experimental period. In addition, no differences were found between control and treated groups in clinical signs, hematology, serum biochemistry, and other findings. Conclusions: In conclusion, above data suggest that no observed adverse effect level of ephedrae herba extract in SD rats might be over 2,000 mg/kg/day in this study.