A novel strain sensor based on poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)-polyvinyl alcohol (PEDOT:PSS-PVA) nanofibers has been fabricated on Kapton substrate by electrospinning, and fully packaged by encapsulating with a polydimethylsioxane layer. Via controlling the concentration of the additive dimethylsulfoxide, the electrical conductivity of the as-spun PEDOT:PSS-PVA nanofiber network can be tuned over a wide rang from 4.8 x 10(-8) to 1.7 x 10(-5) S cm(-1). This kind of strain sensor has excellent stability, fast response, and a high gauge factor of up to about 396. In the meantime, the device could be driven by solar cells, and could detect tiny and quick human actions, for example bending of a finger.