Polycrystalline silicon nanowire field-effect transistor (poly-SiNW FET) has attracted many attentions in the past decade because of its ultrasensitive, label-free, and real-time response for potential sensing applications particular for biosensors. In this paper, the changes of the electric characteristics of poly-SiNW FET introduced by light illumination are studied systematically. Particularly, the red light (635 nm) and UV light (365 nm) are employed as light sources. Both lights are projected on the poly-SiNW FETs installed and are tested in air or in a vacuum (0.1 Torr) chamber. The results show that both light sources can change the electric characteristics of poly-SiNW FET which indicates that the photoelectronic effect can manipulate both n- and p-type devices of poly-SiNW FET; meanwhile, results also support the potential of poly-SiNW FET in air and in the vacuum environment for optoelectronic sensing applications.