The deep-body silverbiddy; Gerres abbrtwiatus, supports an important fishery in the Jaffna lagoon in Sri Lanka. The length-weight relationship and changes in coefficient of condition of this species have been investigated in the present study. The values obtained for the mean weight by sex showed that females are relatively (P>0.05) larger than males. The lengthweight relationships was found to be W = 0.02987xL ^3.04 and W= 0102933x L ^3.05 for males and females respectively and indicated almost isometric growth. Mean Kn values for male and female were almost similar (mean 1.52 +- 0.08SE and mean 1.51 & 0.13SE, respectively). The lowest Kn values from October to February showed the spawning period of the species.