Myricetin is a naturally occurring flavonoid that is commonly found in tea, berries, fruits, vegetables, and medicinal herbs. This study examined the effects of myricetin on the production of interlukin-2 (IL-2), a potent T cell growth factor. Treatment with myricetin significantly inhibited the secretion of the IL-2 protein from mouse EL-4 T cells activated with phorbol 12-myristate 13-acetate (PMA) plus ionomycin (Io) in a dose-dependent manner. Flow cytometric analysis showed that myricetin suppressed the intracellular production of the IL-2 protein. Furthermore, the effects of myricetin on mRNA expression were analyzed by reverse transcription-polymerase chain reaction and it showed that myricetin reduced the expression of IL-2 mRNA induced by PMA plus Io. This suggests that myricetin has potential immunosuppressive effects by inhibiting the production of IL-2.