Length-weight relationships (LWR) were measured for 20 fish species collected during scientific fishing surveys conducted from April 1990 to October 2012 in the Sine Saloum estuary, Senegal, using purse seine and beach seine. The number of individuals collected varied according to the species, from 10 (Hemicaranx bicolor) to 777 (Carlarius latiscutatus). Fish length ranged from 4.5 cm total length (Sphoeroides marmoratus) to 130.0 cm total length (Sphyraena afra). The values of parameter b in the LWR equations (W = aLb where W is weight (g) and L is length (cm)) varied from 2.687 (Hemicaranx bicolor) to 3.334 (Citharichthys stampflii). The coefficient of determination varied between 0.953 (Sphoeroides marmoratus) and 0.996 (Sphyraena afra). The length-weight relationship has never been studied before in Sine Saloum estuary for 13 fish species (Carlarius parkii, Batrachoides liberiensis, Caranx senegallus, Hemicaranx bicolor, Trachinotus teraia, Elops senegalensis, Lutjanus goreensis, Citharichthys stampflii, Psettodes belcheri, Dagetichthys lusitanicus, Sphyraena afra, S. guachancho and Sphoeroides marmoratus). This study provides LWRs that are not available in FishBase (Froese and Pauly, 2020) for 14 species (Carlarius latiscutatus, C. parkii, Batrachoides liberiensis, s Caranx senegallus, Hemicaranx bicolor, Cynoglossus senegalensis, Fontitrygon margarita, Plectorhinchus macrolepis, Pomadasys perotaei, Lutjanus goreensis, Citharichthys stampflii, Psettodes belcheri, Dagetichthys lusitanicus and Sphoeroides marmoratus). It also provides new information for size ranges that are not specified for LWRs in FishBase for 5 species (Ephippion guttifer, Elops senegalensis, Pseudotolithus senegalensis, P. senegallus and Sphyraena afra). In addition, new maximum lengths are presented for Plectorhinchus macrolepis and Citharichthys stampflii. The parameters obtained from this study provide new information for the species studied and will be useful for proper fish population management in West African fisheries.