The NOD-like receptor (NLR) family, caspase recruitment (CARD) domain containing 5 (NLRC5) was dysregulated in endometrial cancer (EC). However, the potential regulatory mechanisms of NLRC5 in EC remained unclear. We aimed to explore whether NLRC5 could regulate the programmed cell death protein ligand 1 (PD-L1) in EC. We also investigated the related molecular which led to the inactivation of NLRC5 in EC. The expressions of NLRC5 and PD-L1 in endometrium tissue microarray were detected by immunohistochemistry. Pearson's correlation analysis was performed to detect the expression correlation between NLRC5 and PD-L1. Immunofluorescence staining, western blotting, and quantitative real-time PCR (qRT-PCR) were used to detect the role of NLRC5 in PD-L1 in EC cell lines. The somatic mutation in EC patients was detected by whole-exome sequencing (WGS). NLRC5 was downregulated in the endometrium of EC patients when compared to those in the normal endometrium. The level of PD-L1 in the endometrium of EC patients was higher when compared to those in the normal endometrium. There was a negative expression correlation between NLRC5 and PD-L1. NLRC5 could promote the expression of PD-L1 in EC cell lines. The mutations of ANKRD20A2, C2orf42, ADGRB3, AVPR2, GOLGA6C, and IPPK may lead to the downregulation of NLRC5 in EC patients. NLRC5 could inhibit the activation of PD-L1 in EC. Mutations of ANKRD20A2, C2orf42, ADGRB3, AVPR2, GOLGA6C, and IPPK may lead to the downregulation of NLRC5 in EC patients. Future study should investigate the mechanism of NLRC5 in PD-L1, as well as the mechanism of ANKRD20A2, C2orf42, ADGRB3, AVPR2, GOLGA6C, and IPPK in NLRC5.