The authors report negative differential resistance (NDR) characteristics observed in nanodevices constructed using three types of fullerenes (C60, C70, and C84) encapsulated metallic double-walled carbon nanotubes. The NDR behavior persists from room temperature (300 K) to lower temperatures, and a significantly high on-off peak-to-valley current ratio is observed for many of the devices examined. The fullerene species exerts a strong influence on the peak voltage of the NDR, which exhibits a linear decrease with increasing fullerene size. The observed current-voltage curves are highly reproducible during measurements, and fully reversible upon change in the bias sweep direction. In addition, the peak current of the NDR is found to increase significantly under light illumination and is recoverable in the absence of light, which indicates potential for applications such as logic optoelectronic devices.