In the present study, length-weight relationships (LWRs) were estimated for three deep sea fish species, namely, Nettastoma melanura Rafinesque, 1810; Lampanyctus crocodilus (Risso, 1810); and Chauliodus sloani Bloch & Schneider, 1801 in the north-eastern Mediterranean Sea. A total of 102 fish samples were collected from Mersin Bay (Erdemli coast). Their length-weight relationship b values ranged between 2.458 and 3.496, and all regressions were found to be significant for all three species (p<0.001). This study is the first reference on length-weight relationships for these three deep-sea fish species from the North-eastern Mediterranean Sea coast of Turkey. Besides, Length-weight relationships for C. sloani and L. crocodilus were not yet available in Fishbase for the Eastern Mediterranean, and hence these results obtained from this study will be useful to re- searchers and fisheries in the field.