The reproductive biology of the ascidian Herdmania momus (Savigny, 1816) was studied at anthropogenic impacted sites along Hurghada coasts, Red Sea, Egypt, during January - December 2013. The specimens of this species were collected monthly from the shallow subtidal zones, and varied from 1.20 to 7.0 cm in total length and from 1.28 to 50 g in total body weight. The results showed that, H. momus is hermaphrodite, carries ovaries and testes at the same individuals, but ovaries are larger in size and shapes than testes. The smallest immature individual has 1.2 cm in length; while the smallest mature individual measured 1.46 cm in length and 1.18 g in weight, with ovaries of 0.041g in weight. The sexually mature individuals of this species have ovaries containing oocytes varied in shapes and sizes, passing through four main stages of maturation reaching stage IV or late vitellogenic stage (ripe ova), with oocytes varied from 100 to 140 µm in diameter, characterized with deep orange color and dense accumulation of yolk granules. It was followed by stage V or spent stage of irregular resorbed eggs. The appearance of ripe ova at stage IV showed spatial and temporal variations. The monthly averages of gonadosomatic indices (GSI) exhibited that, the whole populations of this species at all sites have lengthy breeding season extends nearly all the year around and characterizes with high peaks in gonadal activity during January (6.21), April (6.15), June (6.47), July (6.28), declined slightly in May (5.86), and September (5.15), with remarkably spatial variations at the studied sites. The number of mature eggs or fecundity varied from 1481 to 3724 and averaged of 3082.96±769.96 eggs for all populations. These values exhibited greatly individual variations denoting to partially spawning for each individual. The relationship between total body length (cm) and mean the number of eggs (fecundity) showed an increase in egg number with an increase in animal length