During the course of a screening program for antibiotics produced by a Saccharothrix, two new kinamycins 1 and 2 have been isolated from cultured broth of strain MI293-N4. They inhibit the growth of Gram-positive bacteria and neoplastic cells. This paper describes the production, isolation, purification and the structure elucidation of the antibiotics. Some physicochemical properties and biological activities of these compounds are also reported. Structural analysis using UV, IR, NMR (including 1H, 13C and HMBC) and HR-MS revealed that compound 1 is 3-O-isobutyrylkinamycin C and compound 2 is 4-deacetyl-4-O-isobutyrylkinamycin C. Both compounds inhibit Gram-positive bacteria and exhibit cytotoxicity against L1210 leukemia (IC50: 0.72 μg/ml for 1, 0.38 μg/ml for 2) and IMC carcinoma cells (IC50: 0.88 μg/ml for 1, 0.72 μg/ml for 2) in suspension culture.