The changes in the basic physicochemical characteristics and the lipid composition of Bulgarian organic and conventional dairy products (cow's yoghurt and cow's cheese) during the winter and summer period have been investigated. There were no significant changes in the basic physicochemical characteristics for organic and conventional milk products (fat content in dry matter, content of milk protein, dry matter, acidity, salt content) in the studied periods. Organic yoghurt has lower acidity in comparison with conventional yoghurt. Organic cheese is the only one with a degree of maturity (21.7% and 20.5%), corresponding to the regulated value in the Bulgarian state standards for cheese (not less than 14%). The lipids have identical fatty acid composition, dominated by saturated fatty acids (68.7% -74.5%) and that their content is higher in winter. During the summer period quantities of trans fatty acids in mono- (C18:1) and polyunsaturated fatty acids (C18: 2 and C18: 3) was higher than in winter. The content of tocopherols in the yoghurt fats is minimal, as their values in summer period is higher, such in the various trademarks cheese tocopherols not detected.