The objective of this study was to examine the effects of dietary supplementation of various Dexamethasone (DEX) concentrations on productive and reproductive performance of premature male and female Japanese quails. Japanese quail of 3-weeks-old were received DEX at 0 (control group), 0.25 (low dose treated group) and 0.5 (high dose treated group) mg/kg diet, mixed in their mash, till the 42^th day of age. As a result of this study, in high dose treated group, there were significant (P≤ 0.05) increases in the sex organs weight (g) and laying rate (%) of females meanwhile there was a significant decrease in egg weight and fertility percentage (P≤ 0.001). No significant differences were observed in total testes weight (g) of males but cloacal gland area (mm²) was smaller in both low and high dose male groups compared to control. The serum corticosterone (CORT) level was significantly (P≤ 0.001) higher in low dose treated males whereas no significant changes were recorded in high and low doses treated females. Conversely, a significant (P≤ 0.008) increase in serum estradiol level was measured in treated females but there were no significant changes in serum testosterone level in treated males. The medullary tissues of the adrenal glands were increased on the expense of cortical tissues in birds treated with higher dose of DEX. The seminiferous tubules of the low and high dose treated males did not show all the stages of spermatogenesis and most of the till spermatid stage was inspected with morphologically abnormal cell. The present results concluded that sex differences exist in response to DEX administration prior to reproduction, which may be due to the different prevalence of certain sex steroids influences in specific periods of life.