Silver nanopaticles (AgNPs) and gold nanoparticles (AuNPs) have various applications in medical healthcare and various biological properties such as anti-inflammation, anti-cancer, and anti-angiogenesis. In this study, we investigated the effect of AgNPs and AuNPs on cytokine production via the mitogen-activated protein kinase pathway in leukemic cell lines (T-lymphocytic Jurkat and monocytic U937 cells). We found that both AgNPs and AuNPs inhibited cell proliferation of leukemic cell lines. AgNPs inhibited TNF-α, while AuNPs inhibited interleukin-2 production in Jurkat cells, in which inhibition of cytokines is involved in the extracellular-signal regulated protein kinase but not the c-Jun N-terminal kinase pathway. In U937 cells, AuNPs inhibited interleukin-6 but stimulated TNF-α production in a concentration-dependent manner through the c-Jun N-terminal kinase but not the extracellular-signal regulated protein kinase pathway. Our study showed that each leukemic cell line treated with nanoparticles exhibited a distinct signaling pathway response to inhibit or stimulate cytokine production, leading to anti-cell proliferation. The effects of AgNPs and AuNPs on leukemic cell lines may have a significant impact on leukemia treatment in the future.