Studies of anthracycline antibiotics which have been carried out for the purpose of finding compounds useful in the treatment of cancer are described. Synthetic development of derivatives and analogs which have stronger activities and lower characteristic toxicities than parent antitumor antibiotics such as daunomycin, adriamycin, etc., have been illustrated namely: (1) syntheses of 4'-O-derivatives such as 4'-O-tetrahydropyranyl-adriamycin; (2) syntheses of N-alkyl derivatives such as 3'-deamino-3'-morpholino-adriamycin; and (3) syntheses of 11-deoxy-adriamycin. Notably, 4'-O-tetrahydropyranyl-adriamycin having a (2" R)-configuration has been confirmed to have stronger activity and lower toxicity than adriamycin by Phase II study. New, naturally occurring anthracycline antibiotics (decilorubicin, arugomycin, ditrisarubicin, etc.) have also been reviewed.