A bilayer composite of single walled carbon nanotubes (SWNTs) deposited onto Nafion exhibits substantial mechanical motion upon exposure to visible or near-infrared light. The magnitude of the actuation parallels the absorption spectrum of the SWNTs in the near-infrared, but the actuation diminishes in the visible and disappears in the UV portions of the spectrum. In the near-infrared region, the photoactuation is linear with respect to the light intensity. The photoactuation also appears to be associated with a photocurrent across the nanotube/Nafion interface. The proposed mechanism for the actuation is that band bending of the semiconducting SWNTs induces polarization of mobile hydrogen ions at the Nafion interface, which then causes swelling of the polymer.