The chemical composition and clotting properties of milk from 45 Modicana (Mo) and Holstein (Ho) cows were assessed over the winter (December and January) and spring periods (March-April). The cows came from 4 farms of the Ragusa region (Italy). Considerable differences in milk yield, milk composition and clotting properties were noted between breeds. During the win- ter and spring periods, Mo and Ho produced an average 15.4 and 35.8 kg .day -1 of milk, respec- tively. The Mo milk contained significantly more fat (+5.8 g .kg -1 ), nitrogen (+5.9 g.kg -1 ) and lactose (+1.9 g.kg -1 ). The casein/true protein ratio was also higher in Mo milk (+3.5%) and the plasmin content was 87% lower. The fatty acid composition was the same in both breeds. The pH of the Mo milk was lower (-0.07), coagulation time and curd firming rate were quicker (32 and 53% respectively) and the curd was firmer (+50%). The results obtained during the spring period were very close to those of the winter period. For a same nitrogen content, the Mo milk produced a 16% firmer curd than the Ho milk, probably due to its higher casein/protein ratio and its higher content of casein κ variant B (75 and 28% for Mo and Ho cows respectively). milk / Holstein and Modicana breeds / chemical composition/ clotting properties