The possible use of biodegradable polyethers of microbial origin (polyhydroxyalkanoates) as matrices for deposition of daunorubicin (rubomycin), an antitumor anthracycline, was studied. The tablet dosage form of various rubomycin load (from 1 to 60% w/w) was prepared by cold compaction under pressure. The in vitro kinetics of the rubomycin release from the polymer matrix was investigated. It was shown that the rubomycin release to the medium resulted from the drug solution and diffusion within various periods, from tens hours to several weeks and months depending on the load. When the rubomycin load was under 20% w/w the drug release was prolonged and directly proportional to the observation time. When the rubomycin concentration was under 5%, the drug release kinetics corresponded to the type of the zero order reaction with prolonged release without sharp efflux at the initial stage of the observation. The findings showed that the polyhydroxyalkanoates were applicable as matrices for deposition of rubomycin and preparation of drugs with prolonged action.