Stable water suspensions of copper oxide particles with the mean diameter of 20 nm and copper oxide-copper ones with the mean diameter of 340 nm were used to assess the rats pulmonary phagocytosis response to a single intratracheal instillation of 0.5 mg(1 ml) of these suspensions followed by the bronchoalveolar lavage after 24 hours with the help of optical, transmission electron, and semi-contact atomic force microscopy and a number of biochemical indices measured in the bronchoalveolar lavage fluid. It was found out that the two fractions produce an expressed toxic effect on lungs but nanoparticles appear significantly more toxic than sub-micron particles greater than 100 nm in size while the former evokes a more pronounced defense recruitment of alveolar macrophages and especially of neutrophil leukocytes at a higher phagocytosis activity of these cells. Results obtained compared to literature data show that a high cytotoxic action of nanometer copper oxide particles may be caused both by a copper ions intracellular release at solubilization and direct contact of persistent particles internalized by phagocytes with cell organelles (primarily, mitochondria) and their injuryas well.