Knowledge of the effect of soil nutrients, such as K and Na and their interaction with water availability, on the growth and wood properties of the eucalypts, is needed to increase the productivity of commercial plantation forests in Brazil that generate employment and taxes. The present study evaluates the apparent wood density (at 12% wood moisture) of Eucalyptus grandis trees at 12, 24, 36 and 48 months old under ambient and lower than ambient (66%) rainfall conditions and K and Na nutrient enrichment. The treatments were two water availability (100 and 66% of the rainfall) and the three nutrient treatments were: K (4.5 kmol/ha), Na (4.5 kmol/ha) and a control (natural conditions). The apparent wood density of samples at breast height (1.3 m) was determined by X-ray densitometry and digital images. Increased nutrients at all four ages and water availability at 36 and 48 months reduced apparent wood density in E. grandis trees, however, effects of nutrients are lower under water availability reduction. The radial profile of wood density was higher in four-year-old trees, but there was radial variation in apparent wood density at all ages. These findings predict that, under water stress, apparent wood density will not decline in commercial E. grandis plantations fertilized with potassium. The use of sodium, as a substitute of potassium, should consider their negative impacts on wood density of Eucalyptus grandis trees.