From the cultural broth of a Micromonospora species 25 aminocyclitol antibiotics were isolated by repeated ion-exchange chromatographic processes. The main components of the metabolites were identified as gentamicin C1, C2, and C1a. The other previously reported gentamicin type antibiotics and some other degradation products including gentamicin A, B, B1, X2, sisomicin, garamine, gentamines etc., were identified by chemical, PMR, and mass spectroscopic studies. Besides these, seven new gentamicin type antibiotics were isolated and characterized.