γ-tocotrienol (γ-T3), a tocotrienol isoform belonging to the vitamin E family, has been revealed to exert inhibitory effects on proliferation, migration and invasion in human gastric cancer cells. However, its precise mechanism of action is still unclear and needs to be further tested. Cyclooxygenase-2 (COX-2) is well known for its key role in promoting the migration and invasion abilities of human gastric cancer cells. In light of these data, our study aimed to validate whether the inhibitory actions of γ-T3 could be achieved by downregulation of COX-2 activity in vitro. In the present study, a Cell Counting Kit-8 (CCK-8) assay was performed to observe proliferation in human gastric cancer cells (SGC-7901 and MGC-803 cells), and wound healing and Transwell chamber assays were performed to detect migration and invasion. Western blot analyses were performed to analyse the relative expression of COX-2, matrix metalloproteinases-2 and -9 (MMP-2 and MMP-9) proteins, and enzyme-linked immunosorbent assays (ELISA) were used to determine the exocrine roles of MMP-2 and MMP-9. The results revealed that γ-T3 exerted significant inhibitory effects on proliferation, migration, invasion and COX-2 protein expression, as well as on exocrine functions of MMP-2 and MMP-9 in SGC-7901 and MGC-803 cells. Therefore, our results indicated that γ-T3 exerts inhibitory effects on migration and invasion, which may be mediated through downregulation of COX-2 expression in SGC-7901 and MGC-803 cells.