Miocamycin (MOM) is a derivative of midecamycin, a macrolide antibiotic and is metabolized into 4 main metabolites of Mb1, Mb2, Mb6 and Mb12. At previous study, the acute and subacute toxicity of Mb1 and acute toxicity of Mb2 were performed that those metabolites did not exhibit any lethal toxicity even at the maximum physically applicable dose. The object of this study was to examine subacute toxicity in male and female rats after repeated p.o. administration of Mb2 for 5 weeks at a daily dosage of 125, 250, 500 and 1,000 mg/kg. It is, therefore, concluded that Mb2 exerted no toxic effects in this subacute toxicity.