The aim of this trial was to evaluate the effect of dietary supplementation of extruded linseed on the milk and cheese fatty acid (FA) profiles of ewes under extensive grazing conditions. Over 26 days, a group of nine lactating ewes (Latxa × Milchschaf × Corriedale) in mid-lactation were managed under grazing conditions and given supplements during each manual milking (0830 and 1800 h) of 50% corn and 50% oats (500 g ewe-1 milking-1; control, TC) for the first 6 days. From day 7 to 20, the supplement was 25% corn, 25% oats and 50% extruded linseed (500 g ewe-1 milking-1) (extruded linseed; TEL). From day 21 to 26, the ewes were fed TC. The saturated FA content in milk was reduced (3.6%), and the monounsaturated, polyunsaturated and n-3 FA (7, 10 and 25%, respectively) were increased when the ewes were supplemented with extruded linseed. A correlation between rumenic acid with vaccenic acid (R²=0.68) was found in the milk fat from ewes fed TEL. In cheese obtained from TEL, the contents of n-3 and polyunsaturated FA were increased (21 and 7%, respectively). In conclusion, a supplement of extruded linseed in ewes under grazing conditions could be an alternative lipid source to produce cheese with additional nutritional value. However, the effect of extruded linseed supplementation in ewes under the same conditions with longer experimental periods and a more suitable statistical design must be investigated.