The aim of the present study was to contribute to the geographic distribution and length-weight relationship of Alburnus caeruleus Heckel, 1843 living in the Euphrates and Tigris River basins (Turkey). For this purpose, fish specimens were investigated from the collection preserved in the Istanbul University Science Faculty Hydrobiology Museum (IUSHM). The length-weight relationship was calculated using the equation: W=aL(b). Through sample examinations, A. caeruleus was identified from one new locality (Egri Stream) in the Euphrates River basin and with this contribution, the distribution range of the fish has extended to the tributaries of the Ataturk Dam Lake in the north. The results also contributed to the literature with two new localities of A. caeruleus species in the Savur Stream and River Tigris, both in the Tigris River basin. The b values calculated for the Euphrates and Tigris populations were 3.243 +/- 0.139 (n=56) and 3.340 +/- 0.329 (n=30) respectively, which both indicated positive allometric growth. In addition, the b value was calculated for A. caeruleus from the Tigris River basin is the first finding. This study also reported a new maximum length (TL) for A. caeruleus (13.0 cm).