An object of the present invention is to provide copper nanoparticles that suppress the oxidation of copper, have an average particle diameter of 10 nm or less and therefore undergo a remarkable reduction in the melting point, are highly dispersible, can be sintered at a low temperature, allow the removal of the protective layer during low-temperature sintering at 150° C. or less, and can be suitably used as a conductive copper nanoink material; and to also provide a method for preserving copper nanoparticles, whereby the copper nanoparticles can be stably preserved at room temperature for a long period of time, and can be transported.The present invention provides copper nanoparticles each having a central portion comprising a copper single crystal, and a protective layer surrounding the central portion; (1) the copper nanoparticles having an average particle diameter of 10 nm or less; (2) the protective layer containing at least one member selected from the group consisting of C3-6 primary alcohols, C3-6 secondary alcohols, and derivatives thereof; and (3) the protective layer having a boiling point or thermal decomposition point of 150° C. or less.