Objective To clarify the effect of TRAF2 in the biological behavior of gastric cancer and explore the mechanism. Methods TRAF2 stably depleted AGS cell was established. Cell growth was monitored by x-CELLigence system. Cell proliferation was detected using cell viability assay. The apoptosis and cell cycle were detected by flow cytometry. The difference of migration and invasion abilities were measured by real-time xCELLigence system and Transwell. The expression and activity of NF-κB signaling pathway were measured by western blot and TransAM assay. The expression of TRAF2 in gastric cancer tissue and its clinical significance were detected by immunohistochemistry. Results The cell index of AGS-siTRAF2 cells was significantly lower than that of AGS-sictrl cells at 8 h. In the cell viability assay, the A values of AGS-siTRAF2 cells were 51 296.00±2 631.06, 68 389.25±6 703.21 and 65 559.50±6 339.22 at 24 h, 48 h and 72 h. The values of the viability of AGS-siTRAF2 cells were significantly lower than those of AGS-sictrl cells (P<0.001). The results of flow cytometry showed that the apoptosis rates of AGS-siTRAF2 cells were (1.42±0.07)%, (2.98±0.11)% and (1.56±0.03)% at 24 h, 48 h and 72 h, respectively, which were significantly higher than those of AGS-sictrl cells (all P<0.05). The distribution of S phase in AGS-siTRAF2 cells was (23.57±1.12)%, while that in the AGS-sictrl cells was (19.49±1.19)%. The difference was statistically significant (P=0.012). AGS-siTRAF2 cells migrated much slower than AGS-sictrl cells from 3 h and the number of migrated AGS-sictrl cells was 121.7±6.7 while that of AGS-siTRAF2 cells was 84.0±6.6 (P=0.002). The cell index of AGS-siTRAF2 cells was less than that of AGS-sictrl cells from 3 h. In Transwell assay, the number of invaded AGS-sictrl cells was 109.3±3.1 after 24 h of culture, significantly higher than 79.0±6.2 of AGS-siTRAF2 cells (P=0.002). Western blot analysis showed that the expression levels of RelA, RelB, p50 and p52 in AGS-siTRAF2 cells were significantly lower than those in AGS-sictrl cells. The activities of RelA, RelB, p50 and p52 in AGS-siTRAF2 cells were 0.01±0.00, 0.01±0.01, 0.92±0.01 and 0.53±0.03, respectively, significantly lower than those of AGS-sictrl cells (all P<0.001). High TRAF2 expression (TRAF2-high) was found in 53.0% of GC samples, while TRAF2-high was only observed in 38.0% of the paired adjacent tissues (P=0.033). The expression of TRAF2 was significantly higher in the tubular adenocarcinoma, poor differentiation advanced T, advanced N, and clinical staging (P<0.05). The median survival time were 17 months and 78 months in the TRAF2 high-expression and low-expression groups, respectively, and the difference was statistically significant (P=0.010). Conclusions Depletion of TRAF2 inhibits the AGS cell growth, migration and invasion. The expression of TRAF2 is increased in gastric tumor tissue. The expression of TRAF2 is associated with the prognosis of gastric cancer. [ABSTRACT FROM AUTHOR]