The fiften years of archaeological excavations in Sirmium have already given significant information concerning various spheres of the life in the ancient town. The present paper calls the reader’s attention to what is so far a unique example in our territory: to the existence of three glass melting furnaces within the town. Furnace No 1 has been discovered in the north part of the town (Sector VIII) in a complex of several walls dated to be from the second half of the fourth century. The furnace had been built by the side of wall No III, which wall is older. At a depth of 1.95 m there is first a semi-circular surface of unrefined glass substance in the form of a plate. All around it waste glass particles or bigger pieces, all of irregular shapes, are to be found as well as lumps of raw materials for the production of glass. By the side of the glass plate a fuel-chamber has been discovered, it is made bricks cemented by some muddy substance. The fragments of the Roman bricks used, the cementing by means of mud, and probably also the earthen skull forming the upper part of the furnace indicate a time after the fourth century. This seems to be supported also by a number of various objects from the fifth and from the first half of the sixth century found nearby. The other two glass melting furnaces, which are essentially identical and possibly also simultaneous with the first glass melting furnace, have been discovered in Locality No 28, also in an architectonical complex from the fourth century. These two furnaces are built to the east of wall No XXV, on the premises 15 of the building No V. Both of them are considerably damaged, as they have been discovered in a layer of soil much affected by fire. Furnace No 2 consists of two parts, one of which was probably of a square shape. The floor is covered by fragments of bricks, over which lie thick layers of melted glass. Furnace No 3 is of a rectangular shape, and has only a partly preserved north and south-west wall. On the north wall was probably the opening. The wall No XXV is in its lower part built of bricks cemented by lime mortar and represents the dividing wall of the premise 15 on the Roman locality. Later on, a younger wall was built upon this construction, apparently at the time of building the furnaces with which it is connected. It is built of cracked bricks, cemented by mud or firmly packed earth. Concerning the date of the younger, simpler wall and the date of the glass melting furnaces one can simply say that they are from after the fourth century, and that the upper limit might be posited in the second half of the sixth century — or at the time when the Avars reached the territory of Sirmium.