In this paper, we investigate the transport properties of field-effect transistors (FETs) based on various kinds of fullerene (C60, C 70, and C84) peapods. The encapsulation of various fullerenes inside single-walled carbon nanotubes (SWNTs) is characterized by TEM and Raman spectroscopy. Our results indicate that the transport characteristics of p-type SWNTs are extremely sensitive to the encapsulation of various kinds of fullerene. In the absence of light illumination, the threshold voltage of p-type SWNTs shifts towards positive values after C60 and C 70 encapsulation, and ambipolar transport characteristics are observed for C84 peapods. The photoinduced electron transfer phenomenon is observed for fullerene peapods under light illumination. The optical response for C60 and C70 peapod FET devices is reflected in a shift of threshold voltage towards negative values, and a recoverable characteristic is observed when light is off. After a long period of light illumination, in contrast to p-type C60 and C70 peapods, an n-type transport characteristic is observed on C84 peapods.