©,　2015,　Xi＇an　Medical　University.　All　right　reserved.　Objective:　To　investigate　the　inhibitory　effects　of　docosahexaenoic　acid　(DHA)　and　5-fluorouracil　(5-FU)　in　combination　on　human　gastric　cancer　cell　line　AGS　in　vitro.　Methods:　Human　gastric　cancer　line　AGS　was　treated　with　different　concentrations　of　DHA　and　5-FU　alone　or　in　combination.　The　inhibition　of　cell　proliferation　was　evaluated　by　MTT　assay.　Dose　of　median　(IC50)　of　drugs　(alone　or　in　combination)　and　the　combination　index　(CI)　were　calculated　using　the　median-effect　equation　and　the　combination　index　equation　of　Chou-Talalay.　Flow　cytometry　was　used　to　detect　the　cell　cycle　distribution.　The　expression　of　mitochondrial　respiratory　membrane　protein　complex　in　AGS　cells　was　analyzed　with　Western　blot.　Results:　DHA　and　5-FU　alone　or　in　combination　could　markedly　suppress　the　proliferation　of　AGS　in　significantly　time-dependent　and　dose-dependent　manners　(P＜0.05).　IC50　values　with　DHA　or　5-FU　administered　for　24　h　and　48　h　were　51.60　μg/mL　(DHA:　24　h),　34.82　μg/mL　(DHA:　48　h),　45.90　μg/mL　(5-FU:　24　h),　and　16.86　μg/mL　(5-FU:　48　h),　respectively.　DHA　remarkably　strengthened　the　inhibitory　effect　of　5-FU　and　decreased　IC50　of　5-FU　by　3.56-2.15　folds.　The　combination　of　DHA　and　5-FU　showed　synergism.　Flow　cytometry　showed　that　AGS　cells　treated　with　DHA　and　5-FU　were　arrested　in　G0/G1　phase　and　the　proportion　of　AGS　cells　in　G0/G1　phase　increased　compared　with　that　in　the　control　group,　DHA　group　and　5-FU　group,　while　the　proportion　of　the　cells　in　S　phase　decreased　significantly　(P＜0.05).　Western　blot　showed　after　treatment　with　DHA　and　5-FU　for　48　h,　the　expression　of　mitochondrial　respiratory　membrane　protein　complex　was　significantly　decreased　compared　with　control　group,　DHA　group　and　5-FU　group　(P＜0.05).　Conclusion:　DHA　could　act　synergistically　with　5-FU　in　inhibiting　the　growth　of　gastric　carcinoma　cells,　and　meanwhile　decrease　the　dose　of　5-FU.　The　mechanism　may　be　associated　with　cell　cycle　arrest　in　G0/G1　phase　and　interference　in　the　energy　metabolism　of　AGS　cells　due　to　inhibition　of　the　expression　of　mitochondrial　oxidative　respiratory　chain　complexes　by　the　two　compounds.