Electrospun poly(vinylidene fluoride) (PVDF) nanofibers have shown novel property to convert kinetic energy into electricity. However, most of the PVDF nanofiber energy devices are based on pure PVDF. In this paper, the effect of small molecule doping on PVDF nanofiber diameter, beta phase content, and mechanical-to-electrical energy conversion property is reported. Two chemicals, tri-p-tolylamine (TTA) and 2-(4-tert-butylphenyl)-5-(4-biphenylyl)- 1,3,4-oxadiazole (Butyl-PBD) which have electron-and hole-transfer features, respectively, are chosen as dopants. When the nanofibers contain 0.5% TTA or 1% Butyl-PBD, they show high beta phase content and electric outputs. By combining a layer of nanofiber web which contained TTA with a layer of nanofiber web containing Butyl-PBD, the voltage output is changed to 3.1 V, increasing by approximate to 100% when compared with the single layer nanofiber device of the same thickness. In addition, asymmetric electric outputs are observed in the two layer energy device. These novel features are probably attributed to the high internal polarity across the nanofiber web.