Nuclear factor-κB-inducing kinase (NIK) is a new regulator of nuclear factor-κB signaling, which plays an important role in tumorigenesis. This study aimed to examine the expression of NIK in gastric cancer and investigate its clinical significance.Tumor issues were collected from 80 gastric cancer patients who received surgery and the diagnosis was confirmed by postoperative pathological analysis. The expression of NIK in gastric cancer tissues and adjacent normal mucosa was detected by immunohistochemical analysis. The associations between NIK expression and clinicopathological features of the patients were further analyzed.NIK expression was significantly higher in gastric cancer tissues than in adjacent normal tissues (P < .05). Furthermore, NIK expression showed significant association with UICC stage, T status, and differentiation, but not with age and gender of gastric cancer patients.NIK is overexpressed in gastric cancer and is a potential diagnostic marker of gastric cancer.