The anti-inflammatory effect of n-3 PUFA on the gingivae has already been demonstrated in animal models. The aim of this double-blind, randomized pilot study versus placebo is to evaluate this action in human experimentally-induced gingivitis. For 14 days (D0-D14), 37 healthy volunteers practised intensive oral hygiene, then abstained from brushing their teeth for 21 days (D14 to D35). On D28, the patients were randomized into 2 groups: 18 received the drug (fish oil: 30% n-3 PUFA) and 19 received the placebo (olive oil containing only 1% of n-3 PUFA) at a daily dosage of 6 g (i.e., 1.8 g of n-3 PUFA) 3x for 8 days (D28-D35). The plaque (PI), gingival (GI) and papillary bleeding (PBI) indices were measured on D14, D28 and D35. On D28 and D35, 10 volunteers underwent removal of an inter-dental vestibular papilla, between the 1st and the 2nd superior premolars, to measure out arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA). A gingival biopsy was also taken in another 11 patients, to assay prostaglandin E2 (PGE2) and leukotriene B4 (LTB4). The clinical results of the trial demonstrated, in particular, a significant reduction of GI in the treated group (p < 0.05, Student t-test), but no significant difference between the groups. The biochemical results showed that EPA, DHA and DPA were found in the cells sampled, at higher levels in the subjects taking the drug, with a significant difference for EPA between the 2 groups (p < 0.05, Student t-test). The levels of AA, PGE2 and LTB4 are reduced in the experimental group and increased in the control group, with no significant difference. The LTB4 levels decreased but this difference just failed to reach significance (p = 0.09. Student t-test). This human experimental gingivitis study demonstrated that n-3 PUFA induced a tendency towards reduced inflammation but it was not possible to conclude significant efficacy.