This study investigates for the first time the reproduction biology of Uroteuthis duvauceli in the northern Red Sea, Egypt, over 4 seasons. The sexual maturity was analyzed using the gonad condition in both sexes and by the color of the accessory nidamental glands in females. Spawning season was determined by calculating the gonadosomatic index (GSI) in both sexes as well as the nidamental gland—somatic index in females. Results showed that the spawning season is in winter and early spring. Lastly, the biochemical composition of the mantle in males and females was estimated in the 4 seasons. Lipids, protein, and carbohydrates had a significant difference between the 2 sexes (P < 0.05); however, only protein differed significantly between the 4 seasons (P < 0.05). The seasonal fluctuation of GSI showed a similar trend to the seasonal variation in various biochemical components. In addition to the total lipids and proteins, detailed profiles of each biochemical component are discussed in relation to the sexual maturity of the animal. Also, the morphometric characteristics of males and females of the squid U. duvauceli were investigated. Various body parts were found to have significant difference between the 2 sexes over the 4 seasons (P < 0.01). The analysis also showed that total length has a significant difference in relation to the mantle length between the 2 sexes (P = 0.016). The analysis of length frequency of male and female samples revealed the presence of 2 modes that are assumed to be 2 y classes.