We aimed to quantify the effect of the growth stage of a mountain grassland pasture on the fatty acid (FA) composition of grass and milk. In June (growth) and October (regrowth), a mountain pasture was continuously grazed by six dairy cows in a strip grazing system. During June, the grass C18:3n-3 content decreased while C16:0, c9-C18:1 and C18:2n-6 content increased. During October, the grass FA composition was similar to that observed in the first part of June. During June, milk saturated FA (SFA) content increased while the sum of the trans FA and polyunsaturated FA (PUFA) content decreased, mainly due to the decrease in C18:3n-3 and c9t11-CLA percentages. At the start of October, milk content of PUFA, total trans FA, t11-C18:1, c9t11-CLA and C18:3n-3 was higher than that at the start of June when the grass was still in its vegetative stage. For these FA, the content strongly decreased between the two samplings in October. The variability observed in milk FA composition during one month was high for c9t11-CLA, C18:3n-3, t11-C18:1 and C16:0