A single administration toxicity of (R)-JG-381 was studied in Sprague-Dawley rats of both sexes. In this study, rats were administered orally with dose of 50, 100, 200, 400 and 800 mg／kg of(R)-JG-381. We daily examined number of deaths, clinical signs, body weights and gross findings fur 14 days after (R)-JG-381 administration. When we administered different doses of 100, 200, 400 and 800 mg／kg, we found 5, 3, 5 and 5 male rats and 1, 4, 4 and 5 female rats dead within 1 day after administration, respectively. Some clinical signs(decrease of locomotor activity, decreased respiration rate, lacrimation, prone position) were observed during the experimental period. Our findings suggest that oral $LD_{50}s$(95% confidence limit) for male and female rats are 93.8mg／kg (28.8~161.6mg／kg) and 166.3mg／kg (89. I~284.8mg／kg), respectively.