Regarding the increasing fox population observed today in Belgium as in other European countries, and its repercutions on the efficacy of the fox vaccination against rabies, a study of the red fox (Vulpes vulpes) population has been set up in Southern Belgium. We present the study of the sex ratio, age structure of a fox population of the Belgian Ardenne and evaluate its live expectation. For the period 1996/1997, the age ratio was 100 (juveniles per 100 adults)(n= 140) and the sex ratio 0.95 (male per female)(n= 41). For the period 1997/1998, the age ratio was 104.7 (n= 174) and the sex ratio 1.63 (n= 155). Results are discussed regarding previous works carried out in the South of Belgium and the North of France. The studied population shows a more equilibrated structure than 9 years ago, when oral vaccination programs were started. Consequences concerning the strategy of the fox vaccination are discussed.