This study evaluated the effects of dietary l-glutamine (Gln) supplementation on egg composition and amino acid profiles in laying Japanese quail (Coturnix japonica). A total of 320 birds were assigned to four dietary treatments containing 0.0%, 0.5%, 1.0%, or 1.5% Gln for 12 wk. Eggs were collected at 12 and 19 wk of age, representing the early and late stages of the peak laying period, for analyses of yolk and albumen composition. Dietary Gln supplementation significantly affected the concentration of several amino acids in both yolk and albumen, although the response depended on bird age and Gln inclusion level. The effects were more pronounced in late peak-lay birds and were generally greatest at moderate supplementation levels (0.5% or 1.0% Gln). In albumen, increasing dietary Gln was associated with selective changes in amino acid composition, whereas yolk amino acid responses showed more evident age-dependent patterns. Proximate composition of egg fractions was affected to a lesser extent than amino acid profiles. Overall, the results indicate that dietary Gln modulates amino acid deposition in egg components in an age-dependent manner rather than uniformly enhancing egg nutritional value. This study demonstrates for the first time that dietary Gln supplementation can alter yolk and albumen amino acid profiles in laying quail, supporting its role as a dietary factor influencing amino acid deposition during different stages of lay.