Abstract: The gill ultrastructure of Chu′s croaker Nibea coibor with different body weight (4.75~35.51 g) was studied, as well as the relationship between individual size, life habit and the respiratory area. The results obtained were as follows: the average value of relative respiratory area of the N.coibor was 4.01±1.62 cm² · g^-1. The total number of unilateral gill filament (N)was more closely correlated with body weight(W)(N=28.81+158.45lnW, R²=0.9670, P < 0.01)than with body length(L) (N=17.31L^1.4542, R²=0.8241, P < 0.01).The number of secondary gill lamella(N) per millimeter obviously declined by N=49.971W^-0.3909 (P < 0.01).The single secondary gill lamella area(a) significantly increased by a=0.3199W^0.2528 (P < 0.01), with the increasing of body weight(W).Total respiratory area(A)was significantly positive correlated with body weight(A=11.559W^0.7109, P < 0.01), while relative respiratory area(RA)was significantly negatively correlated with body weight(RA=11.561W^-0.2904, P < 0.01).