The current major way of making nanofibers is electrospinning. However, the minimum fiber diameter is limited to be about 300-500 nm, which is not compliant with the physical definition of nano structures (in the region of 1 to 100 nm). Futher, the productivity is relatively low. This invention provides a method for manufacturing a nano-sized di-block polymer including at least a hard-segment polymer and a soft-segment polymer. First, a sample containing the hard-segment polymer, the soft-segment polymer, and a catalyst is dissolved in a first solvent. Then the dissolved sample is cast on substrate, and then the first solvent to is removed form a dried sample. Finally, the nano-sized di-block polymer is formed by crew-cutting.