Bisoxazolomycin (1), oxazolomycin A2 (2) and oxazolomycin A (3) were identified by physicochemical screening approach from a culture broth of 'Streptomyces subflavus subsp. irumaensis' AM-3603. Compound 2 is a hydrolyzed analog of 3 at the β-lactone ring, and 1 is a new dimeric analog of 2. Compounds 1 and 2 exhibited less potent antibacterial activity and cytotoxicity than 3, which might be due to lack of the β-lactone ring.