We developed a novel straining holder for polymeric materials that is capable of applying large tensile deformation to specimens and performing high-angle tilt for electron tomography. A sample cartridge with a variety of polymeric materials, such as microtomed thin sections of bulk specimens and solvent-cast thin films, can be mounted on the holder. The holder has the following features: large tensile deformation (800 μm) with a large field of view (800×200 μm before the deformation), easy to follow the same field of view and a high tilt angle (±75°) during tensile observations. The strain on the specimen can be applied as large as 26, at least one order of magnitude larger than the predecessor desigined for metallic materials. We demonstrated that deformation processes of isoprene rubber containing silica nanoparticles with this tensile holder.