Fengguo Temple, also known as Seven Buddha Temple or Big Buddha Temple, is an important part of wooden architecture of the Liao Dynasty and is among the first batch of major historical and cultural sites protected at the national level in China. The inner wall of the main hall of Fengguo Temple is painted with large Yuan Dynasty murals extending to the ceiling and shows a Buddha statue of Sumeru Mountain and features a large scale and a high artistic level. They are precious materials for the study of Yuan Dynasty painting arts because of their high artistic and historical value. As an important part of the mural painting layer, the binder plays a vital role in the preservation of murals. Furthermore, the identification of binder sources is also a basis of mural conservation and restoration. Current research on the color painting of murals in Fengguo Temple mainly focuses on the analysis of pigments, but research on binder sources has not been reported so far. Our study focused on the binder of Yuan Dynasty painted murals at Fengguo temple. The amino acid compositions of mural painted layer samples labeled as FGS-1, FGS-2 and FGS-3 were analyzed using gas chromatography-mass spectrometry (GC-MS). In combination with the factor analysis method, the dimension of the multidimensional data matrix obtained from the analysis was reduced, and then the identification of binder sources of Fengguo temple murals was realized. According to the literature, the amino acid composition characteristics of three protein binders commonly used in ancient times are as follows:Animal glue has a special amino acid—hydroxyproline (Hyp) and contains more glycine (Gly); The content of glutamic acid (Glu) in milk is higher and that of alanine was lower; The content of aspartic acid (Asp) in eggs is higher and that of proline (Pro) is lower.  Comparing the analytical results of samples with the above characteristics, we found that the amino acid composition of the samples was close to the characteristics of animal glue—Hyp was found and the content of Gly was high. According to factor analysis, although the scattered points of factor scores of these samples were in the area of animal glue, they were at the edge and even tended to deviate from this area. With the assistance of the factor load matrix, it was found that the reason for this phenomenon was that the Hyp contents in the samples were much lower than that in the reference samples of animal glue. Hyp is easy to decrease due to aging. One of its aging ways is dehydroxylation to Pro; Hyp can also be converted to hydroxyglutamic acid under the action of specific enzymes and oxygen, and then dehydroxylated to Glu. The high content of Pro in FGS-2 may be the result of Hyp dehydroxylation aging. The higher contents of Glu in FGS-1 and FGS-3 may be the results of Hyp enzymatic oxidation. Based on the amino acid analysis results of the samples and the aging patterns of relevant amino acids, it is concluded that the binders of the three relic samples are animal glue, which has undergone obvious aging; FGS-1 and FGS-3 are likely to have bred some microorganisms.  This study provides important information for understanding the technology of making Yuan Dynasty murals at Fengguo temple and also provides a basis for the selection of materials for the conservation and restoration of this kind of cultural relics.