The present invention provides a lithium nickel-layered rock salt-type oxide particle powder, a lithium cobalt-layered rock salt-type oxide particle powder or a particle powder of a solid solution of these layered rock salt-type oxides, wherein the surface of the particle is rendered hydrophobic by coating it with a coupling agent having both a hydrophobic group and a hydrophilic group. The layered rock salt-type oxide particle powder is free of an adverse effect caused by adsorbed water because of less amount of water adsorbed on the surface of the particle powder, high in electrochemical charging and discharging capacities, low in cycle deterioration, so that it is especially useful as a positive electrode active material in a lithium battery.