The influence of a three-year-long foliar fertilization programme on mineral composition of leaf, content of sugars (glucose, fructose, galactose and sucrose) (Prunus avium L.) and organic acids (citric, malic and fumaric acid) of sweet cherry fruits was studied. The experiment was conducted during 2005-2007 in West Hungary on mature 'Germersdorfi 3' grafted on Prunus mahaleb rootstock, planted in 1999 and grown in a calcareous chernozem soil. Trees were foliar-fertilized with potassium (K) as KNO3, calcium (Ca) as Ca(NO3)2 and boron (B) as disodium octaborate tetrahydrate (Na2B8O13 4H2O). Boron spraying was conducted at blooming time and 35 days later. Potassium spraying was carried out 21 and 35 days after full bloom while calcium was applied 21, 35 and 42 days after full bloom. Besides fruit analysis, complete soil and leaf analyses were carried out to study the rate of nutrient uptake and its effects on fruit quality. The applied treatments (except K1) increased leaf K significantly as compared to the control till ripening. Treatments had no consequent effect on leaf Ca till ripening. After ripening, B was present in significantly higher amounts in treated leaf samples. From all applied treatments only boron had a significant effect in increasing sugar contents as compared to the control. Furthermore, repeated Ca spraying had significant effect on the contents of organic acids while B applications led to significantly lower acid contents in the fruit.