The aim of a study was the estimation the influence of the composition of the diet and its supplementation with mineral components, on the concentration of corticosterone and chosen indicators of the water-mineral balance at male rats. Untreated wheat, corn grains, and barley grits in the original diet were isocalorically substituted with wheat flour and sucrose. Analysis of the results allowed to conclude, that the change in diet composition resulted in a significant reduction in the serum corticosterone concentration. Supplementation of the modified diet with selected minerals resulted in a significant increase of the corticosterone concentration, compared to the animals fed the modified diet without supplementation. The change in diet composition and the supplementation applied did not affect the water uptake and urine excretion in the males. On the other hand, differences between the water uptake and the urine excretion were significantly higher in the males fed the modified diet without supplementation, compared to the animals fed the basic diet. The supplementation applied was found to have affected the muscle tissue dry weight of the animals examined.