Plantago asiatica is distributed widely in East Asia. Since ancient times it has been used as a diuretic to treat acute urinary infections, and as an antiinflammatory, antiasthmatic, antioxidant, antibacterial, antihyperlipidemic and antihepatitis drug. The major compound, plantamajoside from P. asiatica, which is used as a marker compound in chemotaxonomic studies, was reported to have antibacterial activity, inhibition activity against cAMP phosphodiesterase and 5-lipoxygenase and antioxidant activity. However, there are no reports on the safety of plantamajoside. This study assessed the toxic effects of plantamajoside concentrate (PC), the purity of which was above 80%, in rats following administration at dose levels of 0, 500, 1000 and 2000 mg/kg body weight/day for 13 weeks, as recommended by the OECD guidelines. The results showed that there were no differences in body weight, food intake, water consumption, relative organ weight or the hematological and serum biochemical values among the different dosage groups. No death or abnormal clinical signs were observed during the experimental period. Therefore, the results suggested that no observed adverse effect level (NOAEL) of the PC in rats after oral administration is considered to be greater than 2000 mg/kg in rats under the conditions employed in this study. Copyright (c) 2007 John Wiley & Sons, Ltd.