Length-weight relationships were estimated for 34 coastal fish species of the Sea of Marmara namely Arnoglosus laterna, Atherina boyeri, Blennius ocellaris, Buglossidium luteum, Callionymus lyra, Callionymus risso, Cepola macrophthalma, Chelidonichthys lucerna, Diplodus annularis, Eutrigla gurnardus, Gaidropsarus meditrraneus, Gobins niger, Lesueurigobius friesii, Lophius piscatorius, Merluccius merluccius, Merlangius merlangus euxinus, Mullus barbatus, Mullus surmuletus, Pomatomus saltatrix, Raja astarias, Raja clavata, Sardinellb aurita, Scorpaena porcus, Serranus cabrilla, Serranus hepatus, Solea kleinii, Solea solea, Spicara smarts, Squalus acanthias, Squalus blainvillei, Syngnathus acus, Trachurus trachurus, Trigla lyra and Uranoscopus scaber. Samples were collected between November 2006 and March 2007 using bottom trawl and commercial beam trawl at depths ranging from 30-100 m. This research is the first reference on length-weight parameters of 21 species for the Sea of Marmara. The parameters of a and b of the equation W = aL(b) were estimated. The b values of the species caught ranged from 1.51 for Cepola macrophthalma to 3.485 for Atherina boyeri. Whenever possible, the b values for the species obtained both in this study and some of the previously reported in the Turkish waters were compared.