Siganus rivulatus, is one of the most economically successful Lessepsian migrant fish, but its reproductive strategy in Egypt needs more studies. A total of 1178 individuals from the Egyptian coasts (the Red Sea; 334, Suez Canal; 353, Mediterranean Sea; 491) were collected seasonally during autumn 2017-summer 2018 to study the important aspects of its reproductive biology. The total length recorded in the Red Sea population (14-28 cm) showed higher values than that in the Suez Canal and Mediterranean Sea (8-22 cm). The sex ratio (M:F) did not significantly vary with the expected ratio (1:1) during all seasons at all sites (chi-square, P˃0.05). Seasonal changes in maturity stages of gonads and values of gonadosomatic index showed that the reproduction of S. rivulatus take place during spring, and extended to summer only in the Red Sea. No significant differences in ova diameter were recorded among sites (ANOVA, P˃0.05). The means of absolute fecundity (F_abs) were 409330, 127497 and 95204 eggs in the Red Sea, Suez Canal, and the Mediterranean Sea, respectively. Relative fecundity (F_rel) was estimated as the number of eggs in ripe ovaries per unit of fish length and unit of fish weight. The F_abs and F_rel of S. rivulatus increased with increasing in fish length (L) and weight (W). Results of F_abs and F_rel displayed significant differences between sites (ANOVA, P<0.05), with higher values in the Red Sea than in the Suez Canal and the Mediterranean Sea.