This communication presents the preliminary results of a new joint project between the Archaeological Museum of Istria and the Centre Camille Jullian for the investigation of a shipwreck discovered in 2015 in the bay of Debeljak, in shallow waters (- 4 m). This bay is situated at the southern tip of the Istrian peninsula (Croatia) within the Natural Park of Cape Kamenjak. Interesting results from the study of the ship structure were gathered in September 2017 and May 2018 will be presented. The ship construction is dated between 380 and 415 AD by AMS radiocarbone dating. The fragments of amphore, found in the surface layera in contact with the déposait, and from the cargo, confirm this late date in antiquity (Late Roman 1 amphora type). The structures uncovered in 2017 correspond to the bottom of the hull. The planning, composed by a large number of planks, is flush laid, carcel built using the typical Greco- Roman assembly system of “mortise and tenons” joints. The frames, spaces on average 17.6 cm, are also composed of a large number of independent eléements, and are connected to the planking by treenails. One floor timber shows a bolt for its assembly to the keel. The keel is not preserved in the area excavated to date. The présence of notches cut into the top of this floor timbres indicate an atypical arrangement of the keelson which is set on the top of a pair of sister keelsons, as documented in other Roman ships dated from the Empire to Late Antiquity. Repairs have been also documented. The shipwreck of Debeljak is particularly interesting within the corpus of the Late Roman maritime shilling vessels of the Mediterranean during a key period for the transition from shell to skeleton shipbuilding.