Background There is rapidly developing interest into the role of several anti‐inflammatory agents to resolve inflammation in periodontal disease. A bioactive polyunsaturated fatty acid, 10‐oxo‐trans‐11‐octadecenoic acid (KetoC), is known to have various beneficial physiological effects; however, the effect of KetoC on inflammation remains unclear. Here, we investigated the effect of KetoC on RAW 264.7 cells stimulated with Porphyromonas gingivalis lipopolysaccharide, and explored the intracellular mechanism responsible for its anti‐inflammatory effects. Methods RAW 264.7 cells were pre‐treated with or without KetoC, and then stimulated with or without P. gingivalis lipopolysaccharide. Levels of tumor necrosis factor α (TNFα), interleukin (IL)‐6 and IL‐1β were determined by real‐time polymerase chain reaction and enzyme‐linked immunosorbent assay. Specific antagonists for G protein‐coupled receptor (GPR)40 and GPR120 were used to clarify the receptor for KetoC. The intracellular mechanism was investigated using western blotting analysis to separate nuclear and cytosolic NF‐κB p65 protein. Result KetoC (5 μmol/L) was not toxic to RAW 264.7 cells, and significantly reduced the expression of TNFα and IL‐6 mRNA and protein, and IL‐1β mRNA. No protein production of IL‐1β was observed. Additionally, when bound to GPR120, KetoC trended to downregulate nuclear NF‐κB p65 protein levels. However, the antagonist for GPR40 failed to diminish the action of KetoC. Conclusion KetoC suppressed the proinflammatory cytokines TNFα, IL‐6 and IL‐1β via NF‐κB p65, by binding to its receptor GPR120. KetoC is a promising candidate in future studies as a bioactive anti‐inflammatory agent in treating periodontal disease.