Background/Objectives: Endometrial cancer is one of the most common gynecological malignancies, with increasing incidence and mortality rates, particularly in developed countries. L1 cell adhesion molecule (L1CAM) has been identified as a poor prognostic factor for human endometrial cancer; however, the molecular mechanisms underlying its role in tumor progression remain unclear. Methods: We investigated the biological significance of L1CAM in human endometrial cancer using multiple cell lines. Functional analyses, including cell proliferation, cell cycle, and apoptosis assays, were performed after L1CAM knockdown or overexpression. Results: L1CAM promoted the transition of endometrial cancer cells from the G0/G1 phase and enhanced cell proliferation. L1CAM knockdown inhibited NF-κB signaling by reducing NF-κB (p65) phosphorylation and downregulating the expression of downstream targets such as TNF. Overexpression of constitutively active IKKβ restored the proliferation defect caused by L1CAM knockdown, supporting the role of NF-κB as a key downstream effector of L1CAM. Immunohistochemical analysis revealed a significant correlation between L1CAM expression and nuclear NF-κB (p65) positivity rates in human patient samples. Furthermore, combination therapy with cisplatin and an IKK inhibitor enhanced the anti-proliferative effect. Conclusions: Our study demonstrated that L1CAM promotes proliferation and chemotherapy resistance in human endometrial cancer through activation of the NF-κB signaling pathway. Therapeutic strategies targeting the L1CAM-NF-κB pathway may represent a promising treatment option for improving prognosis in L1CAM-positive human endometrial cancer.