Several painted clay sculptures in Fengguo Temple in Yixian County, Liaoning Province, showed the severe problem of leaning. A preliminary investigation was conducted, and it was concluded that the inclination was caused by the decay of the wooden skeletons inside the sculptures. With the aim of defining the reason for deterioration of the wooden skeletons, collection of decayed samples in an on-site investigation was carried out, in order to determine the species of the wood samples and the microbes and to identify dead insect corpses. The results show that:1) the two wood samples were hardwood pine (Pinus sp.) and poplar (Populus sp.); 2) there was no wood-decaying fungi, only one strain of the mold, Aspergillus sp. was isolated, and Ascomycota fungi were the main species, according to fungal diversity analysis; 3) insects were identified as Coleoptera beetles, belonging to 4 families, namely Curculionidae, Anobiidae, Dermestidae and Tenebrionidae. Considering that Liaoning is located in the moderate decay hazard zone (D2) in the wood decay hazards map, the primary influence of the deterioration is mainly due to beetles. It is speculated that there was no pretreatment against the larvae and eggs of beetles, or that the pretreatment was not thorough, and later the eggs were hatched and then damaged skeleton wood, finally causing the sculptures to incline. In addition, further investigations show that some columns, beams and other wooden structures in the main hall also had emergence holes with a diameter of about 3 mm, indicating that there is some connection between the sculptures and the building when the biological hazard exists. This research reveals the impact of biodeterioration on the painted clay sculptures and the importance of preventive treatments for wooden skeletons inside the sculptures, and also provides ideas for the preventive conservation and conservation protocols to be designed for clay sculptures in Fengguo Temple and other wooden heritage structures.