BACKGROUND : Ginsenoside compound K (CK), a product produced by the intestinal bacteria-mediated breakdown of ginsenoside, exhibits a wide array of pharmacological activities against diverse targets. However, few of preclinical safety evaluation of CK is reported. OBJECTIVE : The present study therefore sought to assess the toxicity of oral CK in Beagle dogs over a 26-week period. METHODS : All dogs received 4, 12, or 36 mg/kg oral CK doses for 26 weeks with regular monitoring, followed by a 4-week recovery period. Animals were monitored through measurements of temperature, weight, food intake, blood chemistry and hematological findings, electrocardiogram (ECG) measurements, urinalysis, gross necropsy and organ weight and tissue histopathology. RESULTS : Animals in the 36 mg/kg group exhibited an apparent reduction in body weight over the study period, in addition to the presence of focal liver necrosis and increased plasma enzyme levels (alanine aminotransferase, ALT; alkaline phosphatase, ALP) consistent with hepatotoxicity, although there was some evidence suggesting this toxicity was reversible. Animals in the 4 and 12 mg/kg groups did not exhibit any apparent toxicity for any measured parameters. CONCLUSIONS : These results thus indicate that the no observed adverse effect level (NOAEL) in dogs is 12 mg/kg.