[Objectives] Stress response refers to the adaptive mechanism adopted by animals to maintain normal physiological activities when they were subjected to noxious stimuli. It is characterized by the activation of the hypothalamic-pituitary-adrenal axis (HPA axis) and the production of stress hormones, which is corticosterone in most bird species. Artificial propagation plays an essential role in the conservation of Crested Ibis (Nipponia nippon). Nestling period is the key period of growth and development of Crested Ibis. Studying the changes of stress hormones in captive nestlings with age helps to improve the level of feeding management and to provide guidance for field stress physiological research protocols. In this study, the stress response pattern of Crested Ibis was investigated by detecting the plasma levels of the nestlings by the age of different days (23﹣34 d), as well as the effect of sex on this pattern. [Methods] This study was conducted at the Research Center for the Qinling Giant Panda, Zhouzhi of Shaanxi Province, from May to June 2021. Blood samples were collected from 20 Crested Ibis nestlings, ranging from 23﹣34 d to study the variation patterns of plasma corticosterone levels with age in nestlings. All birds were captured and subjected to a standardized capture stress protocol. Blood collected within 3 min was used as the baseline corticosterone level, and blood collected at 15 min after capture was then detected for the stress corticosterone level. We identified sex to preliminarily explore its effect on this pattern. In order to further understand the development characteristics of the stress response of nestlings, we divided the nestling period into the early period of nestlings (23﹣28 d) and the late period of nestlings (29﹣34 d) and collected blood samples of 5 adults. We used Spearman correlation analysis to analyze the correlation between baseline corticosterone level, stress corticosterone level, and age. One-way ANOVA was used to compare baseline corticosterone levels among nestling periods and adults. Mann-Whitney U test and Kruskal-Wallis test were used to compare stress corticosterone levels between nestling periods and among nestling periods and adults. In addition, we use general linear model to explore the effect of sex on this variation pattern. [Results] Our results suggested that there was no significant correlation between the baseline corticosterone level and the age (R = 0.340, P > 0.05). There was a significant positive correlation between the stress corticosterone level and the age (R = 0.492, P < 0.05) (Fig. 3). The plasma baseline corticosterone level of nestlings in the two periods showed no significant difference (P > 0.05), but adults had a significantly higher baseline corticosterone level than these two periods of nestlings (P < 0.01) (Fig. 4). Plasma stress corticosterone levels of nestlings were significantly higher in the late period than in the early period (P < 0.05), and there was a significant difference between the early period and the adult period (P < 0.01), as well as between the late period and the adult period (P < 0.05) (Fig. 5). Sex had no significant effect on the variation pattern of plasma baseline corticosterone level or plasma stress corticosterone level (Table 1, 2). [Conclusion] To summarize, our findings indicated that age did not affect plasma baseline corticosterone levels. Plasma stress corticosterone levels were positively correlated with age. We suggested that human disturbance should be gradually reduced after 23 d of age in the breeding and management of nestlings, and nestlings from 23﹣34 d should be selected in the field stress physiological study.