The a and b parameters of the length-weight relationship (LWR) of the form W = aLb were estimated for 71 species of Actinopterygii and 2 Elasmobranchii, caught in the coastal region and inner shelf of southeastern Brazil. Estimates of b varied from 2.151 to 3.882. For the first time LWR for eight fish species is reported. Significant differences were observed among b values obtained for the same species caught in different ecosystems. Moreover, significant different results for b were observed among species caught in different ecosystems and between sexes of 12 species. Therefore, in order to obtain a reliable biomass estimate it is necessary to choose LWR data close in time and region with estimates for each sex.