1-Furan-2-yl-3-pyridin-2-yl-propenone (FPP-3) has recently been synthesized and characterized to have an anti-inflammatory activity through the inhibition of the production of nitric oxide and tumor necrosis factor-$alpha$. In the present study, adverse effects of FPP-3 on immune functions were determined in female BALB/c mice. When mice were administered orally with FPP-3 at 125, 250 or 500 mg/kg for 7 consecutive days, FPP-3 suppressed the number of antibody-forming cells and reduced thymus weight at 500 mg/kg. In addition, FPP-3 administered mice exhibited reduced splenic cellularity and numbers of splenocyte subsets, such as $CD3^+$ cells, $CD3^+CD4^+$ cells, $CD3^+CD8^+$ cells and macrophages. IL-4 mRNA expression was significantly suppressed by FPP-3 treatment. Moreover, the number of $CD4^+IL-4^+$ cells was reduced following the treatment of mice with 500 mg/kg of FPP-3. These results suggested that FPP-3 at 500 mg/kg might be immunotoxic, and that FPP-3-induced immunotoxicity might be mediated, at least in part, through the inhibition of cytokine production, such as IL-4.