The biodiversity, floristic composition and structure of medicinal plants in the eighteen blocks of Darbhanga were studied. A total of 101 plant species belonging to 32 families, 71 genera and 5 life forms were recorded. Fabaceae, Moraceae, Meliaceae and Apocyanaceae were the overall diverse families (in terms of species richness) of the adult species, contributing 44.5% of all the species in the study. Trees were the most dominant life form (46.5%) followed by lianas (14.8%), herbs (9.9%), epiphytes (7.9%), shrubs (2.9 %) and the others (3.7%). Species richness among all life forms was highest in the DB (90.5%). Fabaceae, Moraceae and Meliaceae and Meliaceae were the most diverse families distributed in all the eighteen blocks of Darbhang The trees in all the forest types studied were generally tall. The difference in height of tree species could be partly explained by degradation in the form of logging of tall and big trees which has undoubtedly affected the vertical structure. Even though tree size (dbh) correlated with tree height in all the forest types, the relationship was stronger (r = 0.741 to 0.368 ; p = 0.000- 0.002 ). Thus, dbh of trees could be a better predictor of tree height. The forest reserve of Mithila looks floristically rich and structurally complex in the face of logging, farming activities and invasion in some parts of the forest. Thus, there is the need to curb the anthropogenic activities and plant invasion so as to protect the integrity of the forest including medicinal plants.