We have isolated a new antitumor antibiotic DC89-A1 with the molecular formula C26H26N3O8Cl from a culture broth of a streptomycete. In this communication, we report the production, isolation, physico-chemical and biological properties of DC89-A1. The producing organism was isolated from soil collected at Mt. Rokko in Hyogo, Japan, and was taxonomically classified as Streptomyces sp. (FERM BP 988). DC89-A1 was isolated from the culture broth via steps including Diaion HP-20 chromatography, solvent extraction, and silica gel chromatography. Its physico-chemical properties are as follows: yellow powder, EI-MS m/z 543, HR-EI-MS confirming the molecular formula C26H26N3O8Cl, UV absorption at 323 nm (ε 23,000) and 415 nm (ε 4,000), IR peaks at 3450, 3300, 1740, 1695, 1620 cm⁻¹, soluble in MeOH, CHCl3, EtOAc, Me2CO, DMSO and insoluble in hexane, water. DC89-A1 showed antimicrobial activity mainly against Gram-positive bacteria. The single dose LD50 in ddY mice was 14 mg/kg with iv administration and 1.2 mg/kg by ip route. It was effective against murine lymphocyte leukemia P388 (showing significant increase of life span at 0.50~0.06 mg/kg ip) and murine sarcoma 180 (T/C = 0.17~0.49 at 4~8 mg/kg iv).