Deformation behavior of CNF nanopaper during uniaxial tensile test was analyzed. The nanopapers were tested in tension, on a universal tensile testing system (Instron 5944, UK) equipped with a 500N load-cell. Specimens were strips 5-6 mm wide. The gauge length was set to 20 mm and the cross-head displacement to 10 %/min. Strain was accurately measured with a video extensometer. Testing was performed in a room at 23oC / 50% relative humidity (RH) and all samples were pre-conditioned for minimum 48h.