A Roman female marble portrait, discovered in 1910 in El Jem is nowadays kept in the Sousse Archaeological Museum. It represent a middle-aged woman with the typical hair-dressing used in the last third of the first century B.C., the so-called nodus or roll-tufted hair on the forehead. Trying to identify the lady, that we can consider, according to the quality and scale of the portrait, as a member of Augustus family, we can therefore underline in the bibliography that there has always been confusion in attributing official carved portraits with such hair-dressing (nodus) to Augustus wife Livia or to Octavia, his sister : the typical idealisation of the augustean portrait— sculpture and the real tendency to have a portrait looking like to the ruling emperor, can often interfere on the individual features of the imperial family members. The researches of V. Poulsen and W.H. Gross have helped to select several groups of Livia's portraits, so that we can notice on another hand the presence, in différents parts of the roman empire, of several portraits of a same lady, showing similar details in features, but having a slightly different hair-dressing from Livia's. She appears young on the heads discovered in Velletri (Rom, Therms Museum), Smyrna (Athens, National Museum) and Glanum (Saint- Rémy-de- Provence), older on the portraits from Béziers (Toulouse Museum), Cerveteri (Ny Carlsberg Glyptotek), Italica (Seville Museum), Naples Museum and Crete (Athens), to which we relate the head of El Jem. The comparative research on the coins, the fact that the same lady took place in two series of julio-claudian family portraits (from Béziers and Cerveteri), and that she is twice represented taller than lifesize, leads us to identify her as beeing Octavia. According to their idealisation standard, their carving technics and comparisons with well-dated portraits of Livia, a chronological order of these portraits can be proposed : the portrait of Smyrna would take place round the time of the wedding of Octavia and Antony (40 B.C.) the one of Velletri round the twenties B.C. The other portraits appear like post mortem realisations inspires from two main types and would extend till Claudius time. The portrait of El Jem, certainly belonging to a dynastic group, take place around the first years of Tiberius rule.