New reports of aquatic insects (Coleoptera, Odonata, Hemiptera, Ephemeroptera and Trichoptera) from Medjerda river basin in Tunisia are presented. 61 species of aquatic insects belonging to 45 genera, 22 families, and 5 orders are listed. 5 species of Coleoptera (Gyrinus (Gyrinus) caspius Ménétries, 1832, Hydroporus marginatus (Duftschmid, 1805), Dryops gracilis (Karsch, 1881), Ochthebius (Ochthebius) pilosus Waltl, 1835, and Hydrochus aljibensis Castro & Delgado, 1999) and two species of Hemiptera (Cymatia rogenhoferi (Fieber, 1864) and Notonecta pallidulaPoisson, 1926) are recorded for the first time in Tunisia. New findings increase the number of Tunisian Coleoptera and Hemiptera to 208 and 38 respectively. A biogeographical analysis shows that the five orders of aquatic insect of the Medjerda river basin are essentially Mediterranean (57%) and Palaearctic (33%) elements, while wide distribution elements are a minority (10%).