Many researches reveal that proteins have the property of piezoelectricity. Therefore, the study presents the concept of energy harvester made of natural spider silk. Moreover, with high density of protein, spider silk can produce more strong and stable piezoelectric property through the polarization technology. The major ampullate gland of native Nephila pilipes was chosen as the silk source in this study, and it was examined by Flourier transform infrared spectroscopy (FTIR), and electrical testing. FTIR reveals the polarized silk increases significantly at the peak of 1610 cm−1 to 1660 cm−1. It means that polarized silk has better α-helix and s-sheet arrangement than non-polarized ones. The result of the electrical testing shows that the output voltage of polarized silk has 3.485 times higher than that of non-polarized silks. Thus, Taiwan local Nephila pilipes spider silks show great potential in energy harvester due to its piezoelectricity.