The microalgae cultivation has been developed over the last decades because it is capable of producing valuable metabolites, such as n-3 fatty acids for nutraceutical purposes. Aim of this study was to investigate the effect of the micro-alga as fat supplement on fatty acid profile of goat and cow milk, with particular reference to n-3 fatty acids and rumenic acid. Twenty dairy goats and 16 dairy cows were randomly allocated to two isonitrogenous treatment groups to investigate the effect of micro-alga supplementation on the composition and fatty acid profile of milk. The 1st goat group was fed with alfalfa hay and concentrate; the 2nd goat group received the same forages but the concentrate was supplemented with 10 g kg-1 DM intake micro-alga. The control group cows were fed with alfalfa hay, corn silage and concentrate, while the experimental animals were fed with the same forages but the concentrate was supplemented with 7.4 g kg-1 DM intake micro-alga. The experimental periods lasted for 17 d. The micro-alga supplements considerably increased rumenic acid concentration in milk (1.20% ví. 1.54%, P < 0.001 for goats; 0.75% vs. 0.85%, P < 0.05 for cows). The n-3 fatty acids were higher in milk (1.02 vs. 1.35; P < 0.001 for goats; 0.47 vs. 0.56; P < 0.05 for cows) and in addition the n-6/n-3 ratio was also more favorable in the micro-alga supplemented groups (3.53 vs. 2.88; P < 0.01 for goats; 4.18 vs. 3.36; P < 0.05 for cows). It is concluded that the diet with micro-alga supplementation significantly increased the concentration of beneficial fatty acids in both goat and cow milk.