This study was performed in order to compare the effect of spawning season on the composition of saturated and unsaturated fatty acids composition, and its relationship with Tenualosa ilisha spawning and maturity stages at coastal waters in Khuzestan. In this research, using gill-nets, 45 fish of ilisha were sampled from Arvandrood and Bahmanshir rivers during a 6- month-period (from winter 2013 to summer 2014), and subjected to biometry. Biometry includes measuring total length and weight of specimens, with analyzing sexual gonads and stages of their gonad maturation based on a 7-step process. Measuring fatty acids was done by a gas chromatography device. Results showed that in females, saturated fatty acids with a binary link (MUFA) in different stages of before (8.43%), peak (9.09%), and after sexual maturation (9.60%) have a significant difference (P> 0.05). In males, a significant difference was observed between peak (9.49%) and after (8.85%) sexual maturation with the stage of before sexual maturation) 10.69 (P>0.05). Female's unsaturated fatty acids with several binary links (PUFA) in peak sexual maturation have a significant difference (0.79%) with before (1.20) and after (0.53%) sexual maturation stages (P>0.05). In males, the amount of this fatty acid in before sexual maturation (0.40%) has a significant difference with peak (0.91%) and after (0.75%) sexual maturation (P> 0.05). In females, long chain unsaturated fatty acids with several binary links (HUFA) in before (4.01%) and peak (4.37%) sexual maturation has a significant difference with the amount of fatty acids in after sexual maturation stage (P>0.05). But in males, the amount of long chain unsaturated fatty acids with several binary links (HUFA) have a significant difference in three stages of before (2.38%), peak (4.48%) and after (3.45%) sexual maturation (P>0.05). Saturated fatty acids in females before sexual maturation (5.84%) stage showed significant difference with peak (77.5%) and after sexual maturation (7.16%) (P>0.05). But in males, there was no significant difference between three stages before (7%), peak (7.11%) and after (7.09%) sexual maturation (P>0.05). Current study results shows that there was a significant difference between fatty acid composition and spawning process in males and females (P>0.05). Females are bigger than males and there is a positive relationship between body size and energy saving, means that increasing body size leads to more energy saving. As a result, increasing body size increases the amount of fatty acids in body tissues.