Eggplant is a Hemafrodite plant from the Solanaceae family and has heterostyle phenomenon (flowering with different style lengths) in flowers. The flowers appear in three forms of high- style, medium- style, and short- style, and about 22-30% of the flowers of the eggplant make up short style flowers. Flower morphology and style length are one of the factors limiting the pollination, fertility and fruit formation in eggplant. Studies confirms the role of hormones in improvement of the flowers heterostyley in eggplants. Research has shown that polyamines (including spermidine,spermine and putresin) play a role as plant growth regulators in processes such as flowering, growth and development of the reproductive organs, the formation, growth and ripening of fruits. This research was carried out to investigate the effect of spermidine and its synthesis routes on flowering and fruit formation in two early and late flowering genotypes of eggplant during two experiments in a completely randomized and semi-experimental factorial design in greenhouse of Isfahan University of Technology. The first experiment consisted of genotype factor (two early and late flowering genotypes) and chemicals (1 mM spermidine, 0.5 mM spermidine, two compounds inhibiting the spermidine synthesis route and control) in order to investigate the effect of external spermidine on flowering and fruit formation. In the second experiment, two first experiment genotypes and treatments consisted of two concentrations of one and a half milimolar spermidine, three inhibitory treatments with a concentration of 3 mM and methionine amino acid at a concentration of 200 mg / L and control treatment (distilled water) to study the flowering mechanism in two early and late flowering genotypes of eggplant was taken. Treatments were applied in three stages of vegetative growth, beginning of flowering and 10 days after flowering. Spermidine increased the traits such as plant length, number of lateral branches, length of style, percentage of high style flowers, percentage of fruit composition and yield. The highest plant height was observed in 0.5 spermidine treatments in both cultivars and the lowest in the combination of two inhibitors of early flowering genotypes. Also, the highest number of days to flowering was observed in the combination treatment of two inhibitors of late flowering genotype and its lowest in spermidine treatment of 0.5 early flowering genotypes. The highest fruit weight and yield were related to 1 mM spermidine treatment and the late genotype, and the least of them was observed in the combination treatment of two inhibitors in the early genotypes. The result of this study was that spermidine was an effective treatment for the improvement of flowering and fruit characteristics in two genotypes. The results of the second experiment indicated that in the late flowering genotype, the blocking of the methionine precursor path had more inhibitory effects on reproductive and fruiting characteristics, and it could be said that the pathway was more active in flowering and fruiting of this genotype. In early flowering genotype, flowering traits, such as the late flowering genotype acted on, but in the case of the traits of fruit, the effect of spemidine has been shown to be lower in the genotype, and perhaps the pathway is more active in this regard. Finally, based on the results, it can be argued that the activity of synthetic pathways and their effects on different processes depends on the different cultivars and stages of the development of the eggplant. Keywords : Eggplant, heterostyly, polyamine,syntesis inhibitors