Copper is required for normal functioning of all basic biochemical and physiological processes in the body. The objective of this study was to compare the effect of two different chemical forms (carbonate and nanoparticles) of Cu administered in feed mixtures to growing rats on bone geometric and structural parameters as well as material characteristics in a rat model. For this purpose, five experimental treatments were used to evaluate the effects of different levels of Cu applied in the diet as a mineral mixture (the standard dose of 6.5 mg/kg diet, half the standard dose, and no Cu in mineral mixture as a negative control) and two Cu sources (CuCO3 – commonly used in rodent laboratory diets and a Cu-NP nanoparticle preparation, 40 nm). There were no changes in body weight and bone morphology, but significant alteration was noted in the geometry and mechanical parameters, which was Cu-NP-dose dependent. Our study showed an increase in the ultimate load and toughness in Cu-NP-treated rats at the standard concentration. The higher values of the studied parameters prove that there was a change in bone mineralization. Although bone mineral density and content were not changed, bone tissue density and ash increased. The XRD analysis revealed that some peaks did not originate from hydroxyapatite, and they indicated existence of other mineral phases. No studies conducted so far have provided a detailed mechanical X-ray diffraction analysis of bone tissue of growing rats administered with diet containing Cu nanoparticles. This study showed that Cu-NP given in low dose increased mechanical endurance of bone, without the changes in strain and stress compared to low dose of Cu given in traditional form