This study investigated the potential of pinon shell polysaccharide (PSP) to enhance immunity against H9N2 subtype avian influenza virus (H9N2 AIV) in chickens. The effect of PSP treatment and H9N2 virus infection after PSP pretreatment were investigated by [3-(4, 5-dimethylthiazol-2-yl)-2, 3-diphenyl tetrazolium bromide] assay and analysis of major histocompatibility complex and cytokine mRNA expression. The in vivo effects on lymphocytes and serum antibody titers were also investigated. The IL-6 expression and antibody titers were enhanced in the first week after PSP treatment. These data indicate that prophylactic PSP administration reduces H9N2 AIV replication and promotes early humoral immune responses in young birds.