Antitumor antibiotics rhodilunancins A and B were isolated from a culture of Streptomyces violaceus var. lunanensis var. n. No. 1289 by acidic acetone extraction of mycelia and purified by silica gel chromatography.Rhodilunancin A is identical to cosmomycin A. Rhodilunancin B is identical to cosmomycin B (=rhodomycin Y). Both antibiotics exhibited activities against Gram-positive bacteria and inhibition on DNA synthesis of P353 leukemia cell in vitro.In the course of our screening for new antitumor antibiotics, a Streptonryces strain, Streptomyces vioaceus var. lunanensis var. n. No. 1289 isolated from soil sample collected at Lunan county, Yunnan province, was found to produce two anthracycline antibiotics, rhodilunancins A (I) and B (II) (Fig. 1). Strain No. 1289 was cultured in a fermentor containing a medium of the following composition: soluble starch 1.5%, dextrin 1.5%, glucose 1.5%, soybean meal 1.2%, peptone 0.5% yeast extract 0.5%, (NH4)2SO4 0.25 %, NaCl 0.2 %, KH2PO4 0.02 %, CaCO3 0.3 %, MgSO4 0.02 %. The cultivation was carried out at 28°C for 4 days.The antibiotics in the mycelia were extracted with acidic acetone. The extracts were concentrated in vacuo to remove acetone and reextracted with ethyl acetate. The basic glycosides were separated from the aglycone by extraction with aqueous acid (pH 3). The acidic solution was adjusted to pH 8