[Objectives] The reproduction management of captive female Giant Pandas Ailuropoda melanoleuca is crucial for ex-situ conservation in Giant Pandas. The primary difficulty in reproduction management is to determine when female Giant Pandas are in estrus. However, the current methods for determining estrus have many limitations, such as susceptibility to observers’ experience or other subjective factors, complicated operation, and high costs. This study investigated the changes in daily fecal weight of 30 captive female Giant Pandas during the 31-d pre-mating period (31 d before the day prior to natural mating or artificial insemination) and analyzed their relationship with the estrus initiation, as indicated by changes in estrogen and progesterone levels, aiming to provide a new perspective for assessing estrus initiation and improving reproduction management. [Methods] A total of 1 168fecal samples from 30 captive female pandas (aged 5﹣20 years old) over 38 pre-mating periods were collected daily. The samples obtained at 15:00 and 09:00 the next morning were combined and weighed together as the daily fecal weight by a TCS-150 electronic platform scale (capacity:150 kg, division:10 g, accuracy:± 10 g). Urinary estrogen and progesterone levels were monitored via enzyme-linked immunosorbent assay (ELISA) to determine the date of hormone initiation. Temporal patterns of changes in fecal weight were modeled through 5th-degree polynomial regression (Python 3.10.9 with numpy 1.23.5), with elbow points of the weight decrease identified via the KneeLocator method (Python 3.10.9 with kneed 0.8.3). We employed the Wilcoxon signed-rank test (Python 3.10.9 with scipy 1.10.0) to statistically analyze the changes in fecal weight, with a significance level set at P < 0.05. [Results] The results showed that (1) the elbow point of fecal weight decrease (17.5 ± 4.8 d before mating) appeared about 8 d earlier than the hormone initiation (9.2 ± 2.3 d before mating) (T = 6.5, P = 2.0 × 10^﹣7). Fig. 2 presented the polynomial curve fitting of changes in fecal weight in the 38 pre-mating periods, and Fig. 2 and Table 1 indicated the elbow points and the time points of hormone initiation; (2) the time of the fastest fecal weight decrease (9.8 ± 5.6 d before mating) between the elbow point and the 3rd day prior to mating coincided with the hormone initiation time, with no significant statistical difference observed (T = 313.5, P = 0.99). Table 1 detailed the time points of the fastest fecal weight decrease and hormone initiation; and (3) there was a significant difference in the standard deviation of fecal weights that could be used to distinguish whether Giant Pandas gave birth or not after mating. Specifically, during the phase of stable fecal weight (31﹣18 d before mating) and the phase of fecal weight decrease (17﹣1 d before mating), the P-values were 2.3 × 10^﹣3 and 1.5 × 10^﹣5, respectively. Fig. 3 illustrated the mean values and standard deviations of daily fecal weight during the 31-d pre-mating period for Giant Pandas that would give birth and those that would not, and Table 2 presented the statistical significance in fecal weight between the two groups. [Conclusion] These results provide new perspectives and methods for assessing the timing of estrus initiation and reproductive outcomes in captive female Giant Pandas, which will help to expand the preparation time for reproduction management and improve reproduction success of captive Giant Pandas through precise resource allocation.