This study was conducted to evaluate the repeated dose toxicity of DA-1131/betamipron, newly developed carbapenem antibiotic, in rats. DA-1131/ betamipron was administered intravenously once a day for 4 weeks to 10 males and 10 females per group at the doses of 0(control),40, 160 and 640 mg/kg. Throughout the study period, all rats survived. The administration of DA-1131/betamipron induced soft stool or diarrhea in rats of both sexes receiving 160 or 640 mg/kg. The water consumption was increased with a statistical significance in 640 mg/kg during observation period. At the end of administration, hematological and serum biochemical examination showed no toxicological changes in DA-1131/betamipron treated groups compared with control group. Histopathologic examination revealed inflammatory cell infiltration, tubular dilatation and focal necrosis of kidney in two males and three females in 640 mg/kg. On the basis of these results, the noobserved-adverse-effect-level of DA-1131/betamipron was estimated to be 40 mgtg under the present test condition.