The reproductive biology of the Sea urchin Tripneustes gratilla from Hurghada, Red Sea, Egypt was studied in the period from January 2018 to May 2019. The specimens were collected monthly at a depth ranging from 1 to 2.5m. This study introduced data based on the monthly estimation of the gonadosomatic index and the monthly occurrence of each maturity stage relative to the total number of examined gonads. The oocyte size frequency distribution and the histological examination of the gonads of both sexes were used to describe the maturity stages. The results revealed that both males and females showed synchronization in the reproductive cycle. The highest values of gonadosomatic index (GSI) were recorded in October for both sexes and exhibited a decline in November which indicates that spawning took place in this period. Tripneustes gratilla population in the Red Sea showed a restricted breeding season that extended from October to February. The egg diameter varied from 4 to 60 microns throughout the gametogenic cycle.