Rheum emodi has been used as an edible and medicinal plant in Tibet and Kashmir for a long period of time, while safety evaluation of this plant has not yet been investigated. In this study, acute and subchronic oral toxicity studies of aqueous extract of R. emodi (AERE) rhizome were conducted in SD rats. Animals were treated with a single dose of 1000, 2000, 4000 or 10,000 mg/kg of AERE in the acute toxicity. In subchronic oral toxicity, animals were randomly divided into four groups (10 rats/sex/group) and received doses of 0, 1000, 2000, and 4000 mg/kg/d of AERE for 90 days. Daily clinical observations, weekly measurement of body weight and food consumption were conducted. Blood and urine were collected on days 91 to measure changes. At necropsy, selected organs were weighed and recorded, and histological examination was performed. During the subchronic oral toxicity study, no mortality, obvious treatment-related clinical signs and urinalysis parameters were observed. Differences in weight gain, food consumption, hematology, biochemistry, relative organ weight and histopathology examinations between the treated group and the control group were not considered treatment-related. Our results indicated that the no-observed-adverse-effect level (NOAEL) for AERE was 4000 mg/kg/d in both genders.