Soluble gonad protein for both sexes of Siganus rivulatus was analysed by isoelectric focusing in seven maturity stages. Sex- specific electrophoretic and isoelectric focusing patterns were found. More protein fractions are identified for stage II of both sexes than for die other stages. The total number of protein bands for female was greater than those of male. In female, spawning stage has the maximum number (4) of specific band while in male the maximum ones (6) were separated from stage (HI). The number of common bands in both female and male was (3 & 2) respectively. Clear differences in protein patterns of the seven stages for both sexes can be used to characterize the breeding season.