Buildings of significance in the ancient city of Kos include the now restored Roman Odeon. It lies at the south of the western archaeological site, to the west of the also restored Roman villa (Casa Romana) and to the northwest of the ancient theatre. According to information from ancient inscriptions, the odeon replaced the precedent public building probably used for the assemblies of the citizens of Kos and perhaps serving as the bouleuterion (council chamber) of the town. The odeon was built between the first and second century AD to host music competitions; it was also the seat of the Gerousia, the public authority of Kos, having no political power, as stated by inscription testimonies, but ensuring the attribution of honours to distinguished citizens of the island.

The building was initially roofed and seated approximately 750 persons. Its cavea with a northern orientation was supported by arched constructions built on pillars of caster masonry (opus caementicium). It had fourteen rows of marble seats, nineteen of which have been restored, and was divided by a corridor into two sections; the cunei of the lower section were divided by four staircases. Under the cavea lied two semicircular porticos and a series of rooms used as shops or workrooms. The form of the scene was unusual: an irregular pentagon made of two parts, the proscenium (front of scene) and the paraskenio (backstage), communicating thanks to three entrances. On both sides of the scene were two more doors leading to the parodoi (passageways). The floor of the circular orchestra was decorated with opus sectile (marble works), while mosaic floorings adorned the parodoi. The inner galleries of the Odeon were decorated with marble statues initially standing in niches; the most notable is that of Hippokrates, today exhibited at the Archaeological Museum of Kos.

The excavation of the odeon was carried out in 1929 by the Italian archeologist L. Laurenzi. The first phase of restoration conducted by the Italian Archaeological Expedition started in 1929; between 1994-1999 new restoration works were undertaken by the Twenty-Second Ephorate of Prehistoric and Classical Antiquities and by the Directorate for the Restoration of Ancient Monuments. In recent years there are efforts to highlight the surrounding area, as well as to house an internal photographic exhibition; these are financed by the Third Community Support Framework and conducted by the Archaeological Institute of Aegean Studies. At the same time, the odeon hosts at intervals cultural events organized by local authorities of the island.