The Archaeological Museum in Leros, housed in the neoclassical listed building of the old Civic School in Agia Marina was built in 1882 as a boys' school with the sponsorship of the Lerian Brotherhood of Cairo.

The permanent exhibition of the museum provides a vivid picture of the history of Leros; it begins with finds from the prehistoric sites of the island, proceeds to the historic period and focuses on the political affiliation of the island with Miletus, and presents the local religious customs and funerary practices. The exhibits include typical examples of pottery and sculpture (clay masks of Dionysus, female bust, figurine of a symposiast), resolutions from the 3rd and 2nd century BC, funerary offerings including red-figyre piriform aryballoi and Roman perfume  jars, archaic bronze buckles, a glass alabaster and amphorae from Chian and Rhodian workshops.

The excavation of the Early Christian basilica and the secular building in Partheni yielded many archaeological objects, including coins, fragments of frescoes , mosaic dedicatory floor inscriptions and stone architectural members. This section of the exhibition dedicated to medieval times refers to the most important monument of this era on the island, the castle of Panteli, whose history and architecture is presented through drawings, photographs and visual material. The exhibition concludes with finds (crossed, blessing talismans) for pilgrims and travelers who visited Leros, objects from the known "Milesian islands", and pottery.