Conjugated linoleic acid (CLA) is a naturally occurring anti-carcinogen compound found in dairy products. A survey was carried out during the years 2000-2002 in South Sardinia, on a total of 15 dairy sheep farms characterised by different pedological conditions, pasture composition and supplementation levels. Samples of bulk milk and cheese, produced in the same factory, were collected monthly, during the milking period, and fatty acid composition, inclusive of CLA was determined. Data of feeding management were also recorded every month and hand-plucked samples of main forage species on offer were taken. The level of CLA in milk was high (18.46±0.93 mg/g of fat), when the flocks grazed pastures at vegetative phase while it dropped down to 13.34±1.67 mg/g of fat during pasture reproductive phase. The same trend was found in the content of precursors like linolenic acid in some grazed species that markedly declined (about 50%) in the reproductive phase. The level of supplementation tended to negatively affect the milk CLA content. Similar effects of pasture maturity and supplementation levels were shown on the CLA content of manufactured cheeses. In conclusion, the level of CLA in milk and cheese was positively related with the amount of sheep requirements covered by the grazed herbage.