CCRF-CEM and Jurkat E6-1, human T cell leukemia, produced interleukin (IL)-2 stimulated with phorbol myristate acetate (PMA) and pokeweed mitogen (PWM). IL-2 cytokine production and mRNA expression of CCRF-CEM were increased by treatment with kaempferol, a tea (Camellia sinensis L.) flavonol, while those of Jurkat E6-1 were decreased by kaempferol treatment. We therefore investigated the nuclear factor expression of activated T cell (NFAT), a critical regulator of IL-2 gene transcription during T cell activation. In CCRF-CEM, NFAT induction of cytoplasmic extract and NFAT translocation to the nucleus were increased by kaempferol, demonstrating that kaempferol might affect the upstream cascade of T cell signaling. However, in Jurkat E6-1, NFAT induction of cytoplasmic extract was normal, but NFAT translocation to the nucleus was decreased by kaempferol treatment. In this report, it is demonstrated that kaempferol has different effects in the T cell signaling cascade.