Ultrafine fibers containing water-soluble drugs were successfully electrospun from water-in-oil (W/O) emulsions, in which the aqueous phase contained the water-soluble drugs and the oily phase was a chloroform solution of amphiphilic poly (ethylene glycol)-poly (L-lactic acid) (PEG-PLLA) diblock copolymer. The diameter of the electrospun fibers was in the range of 300 nm-1 microm. A water-soluble anticancer agent, doxorubicin hydrochloride (Dox), was used as the model drug. Its content in the fibers was 1-5 wt.% and it was entirely encapsulated inside the electrospun fibers. Its release from the fibers was controlled by the combined diffusion mechanism and enzymatic degradation mechanism. At the early stage, the diffusion mechanism was predominant and a certain time later, the enzymatic degradation mechanism became predominant. The antitumor activity of the Dox incorporated in the PEG-PLLA fibers against mice glioma cells (C6 cell lines) was evaluated by MTT method. The results showed that the Dox could be released from the fibers without losing cytotoxicity.