The study focused on the evaluation and characterization of plant genetic resources of fodder legumes in northern Tunisia for the purpose of biodiversity conservation. The study was carried out on the biodiversity of legumes (Fabaceae) and their geographical distribution as well as on the ecological characterization of their natural environment using different ecological indices. Nine sites distributed in the governorates of Bizerte, Beja and Jendouba were visited to collect information. In this context, an inventory was carried out showing the presence of 40 different species of forage legumes divided into 15 genus, some of which exist in the three governorates prospected at the same time. The genus Trifolium and Medicago was the most diversified by the presence of 9 and 8 species. Thus, eight less diversified monospecific genus have been listed such as (Anthyllis, Calicotome, Hippocreppis, Lathyrus, Lupinus, Melilotus, Scorpiurus and Retama). We have also identified species with widespread distribution such as Trifolium campestre and Trifolium tomentosum and species with restricted geographical distribution such as Anthyllis vulneraria at Rimel in the governorate of Bizerte and Hippocreppis unisiliquosa in the governorate of Beja in Medjez El Bab. Shannon index showed differences between and within governorate. The three governorates studied have an average of 1.883 bits in Bizerta, 2.052 bits in Beja and 1.601 bits in Jendouba. This shows that diversity index is significantly higher in Béja compared to that of Bizerte and Jendouba. Jaccard similarity index calculated for the different studied localities.