Fentanyl is used as an analgesic to treat pain in a variety of patients with cancer. Moreover, fentanyl may affect tumor growth in many cell lines. To gain better insight into the interaction between fentanyl and tumor, we investigated the effects of fentanyl on the growth of gastric carcinoma cells and the expression of some apoptosis-related genes including NF-kappaB and PTEN. A human gastric cancer cell line MGC-803 was used. The viability and proliferation of gastric cancer MGC-803 cells were detected by MTT assay and colony formation assay. The cell cycle progression and apoptosis were assessed by flow cytometry and the ultrastructure of cells was examined with transmission electron microscope. The migration of cells was investigated by wound healing assay. The expression of NF-kappaB and PTEN was evaluated by semiquantitative RT-PCR and Western blot. Our data showed that fentanyl could inhibit cell growth and proliferation and made cell cycle arrest at G2/M phase. Compared with control cells, MGC-803 cells that were incubated with fentanyl also had a higher apoptotic rate. Fentanyl could lead to morphological changes of gastric cancer cells and reduce the motility of MGC-803 cells. Moreover, fentanyl could downregulate NF-kappaB and upregulate PTEN, which might be the mechanism of fentanyl inhibiting gastric cancer progression in vitro.