Chitosan, a polymer of D-glucosamine, is a polysaccharide derived from the chitin found in the exoskeleton of shellfish, such as shrimp or crabs. The effects of chitosan has been recognized that chitosan-fed farm animals demonstrated higher weight gains but less incidence of diseases than the unfed ones. However, these beneficial effects has not been elucidated clearly. In this study, we examined the modulatory effect of chitosan and D-glucosamine on the expression of porcine cytokines in vitro. Porcine spleen cells were cultured in the presence of chitosan and D-glucosamine, and the effects of chitosan on the cytokine mRNA expression were evaluated. Expressions of IL-2 and IFN-gamma were increased in the chitosan-treated porcine spleen cells. Expressed cytokines in the D-glucosamine-treated cells were IL-2, IFN-gamma, and IL-12 p40 subunit. In particular, IFN-gamma was expressed more efficiently, and D-glucosamine was more effective for expressing the cytokine gene. These results suggest chitosan as well as D-glucosamine could induce the expression of cytokines as Th1 subset such as IL-2, IFN-gamma.