Nanocapsules based drug delivery system has provided an efficient tools in cancer treatment in recent times. The toxicity of anticancer drugs can be decreased through nano-encapsulation using polymeric nanocapsules. This study aimed to synthesis, optimization and characterization of doxorubicin (Dox) loaded biodegradable polycaprolactone (PCL) nanocapsules. Dox loaded PCL nanocapsules were prepared by double emulsion method using dichloromethane as the organic solvent, and polyvinyl alcohol as the external aqueous phase. Formulation parameter such as the effect of weight ratio of drug to polymer was optimized for the synthesis of Dox-PCL nanocapsules. Different weight ratio of Dox loaded PCL nanocapsules (1:20), (1:50) and (3:10) were prepared. Dox-PCL nanocapsules of weight ratio of 3:10 mg had higher DL of 16.88 % than other cases and its average size determined by dynamic light scattering (DLS) was 212 nm. The TEM image revealed that the prepared nanocapsules were spherical in shape in all cases. Also, ZPs were greater in case of Dox-PCL with ratio of 3:10 mg than other cases, which suggests good stability these synthesized nanocapsules. Finally, these results indicate that the properties such as DL %, morphology, size and surface charge of the nanocapsules colloidal suspension were better with decreasing the amount of PCL and increasing the amount of Dox.