Sintering behavior of copper nanoparticles with a protective layer of gelatin synthesized by wet-chemical process with an average diameter of 45 nm has been observed using in-situ transmission electron microscopy (TEM). Copper nanoparticles were sublimated without sintering at about 925 degrees C at 2.0 x 10(-)(5) Pa, and carbonized gelatin remained and retained the shape of the initial layer of nanoparticles. Copper nanoparticles were sintered without sublimation at about 250 degrees C with between 1.0 x 10(-)(4) and 6.0 x 10(-)(4) Pa of oxygen gas flow. It was found that the surface of the sintered copper was covered by a gelatin layer.