Cu nanoparticles capped with fatty acids and amines were developed as low-temperature sintering materials. The fatty acids and amines used were decanoic acid + decyl amine (C10) and oleic acid + oleyl amine (C18), respectively. The synthesized Cu nanoparticles were analyzed using X-ray diffraction, transmission electron microscopy, and thermogravimetric and differential thermal analysis. Because both of the capping layers could be decomposed at temperatures lower than 300°C even under an inert atmosphere, bonding and sintering experiments could be carried out in the absence of oxygen to prevent the oxidation of the Cu nanoparticles. The sintered structures were observed using scanning electron microscopy. The shear strengths of Cu plates bonded using the C18 Cu nanoparticles were larger than those of plates bonded using the C10 Cu nanoparticles. At 300°C, the strength was higher than 30 MPa, and of the same order as ordinary high-temperature solders, even though the processing temperature was low. The resistivity of a film sintered using the C18 Cu nanoparticles was 12 μΩcm at 300°C, which was lower than the values reported in previous studies.