We examined the types of marriage between husband and wife and their frequency as well as the intensity of consanguinity for the Mauritanian ethnic groups. Then we evaluated for all the population, the variations of each of these dimensions according to the dates of marriage. The analisys of a sample of 2413 couples obtained according to the quota method showed that the Mauritanian population presents a strong family endogamy of about 47.20%. The Wolofs and the Poulards present pourcentages of marriages between blood relations of about 74.47% and of 55.74% respectively. On the other hand, for the Maures, black Maures and Soninkes, the proportions of marriages between blood relations are of the order of 41.25%, 30.52% and 46.99% respectively. This same analysis has also shown that the Mauritanian ethnic groupes present high apparent coefficient of consanguinity. They are of a level of unions between unequal cousins (1 /32) for (1/64) for others. The evaluation of endogamy practices in function of marriage dates (from 1921 to 1991) shows and for all the population a decline tendency in the pourcentages of consanguine marriages, and at the level of a whole Mauritanian population.