We examined effects of N-acetyl-D: -glucosamine (GlcNAc) on rheumatoid arthritis (RA) mouse models and effects of GlcNAc and glucosamine hydrochloride (GlcN) on several serum cytokine productions in RA mouse models. SKG/jcl mice were divided into control, GlcNAc, and GlcN groups. For 56 days, the control group received normal food, the GlcNAc group received 0.5 % GlcNAc-containing food, and the GlcN group received 0.5 % GlcN-containing food. GlcNAc and GlcN equally suppressed arthritis scores and histopathological scores compared to the control group. In the GlcN group, serum tumor necrosis factor-α and interleukin (IL)-6 concentrations were significantly decreased compared to the control group. In the GlcNAc group, serum IL-10, transforming growth factor β-1, and IL-2 concentrations were significantly increased compared to the control group. Our results indicated that GlcNAc also has suppressive effects on experimental RA in mouse models. The results of serum cytokine concentrations suggested that compared to GlcN, GlcNAc has a different suppressive mechanism in experimental RA models.