Cyclin A2 plays critical role in DNA replication, transcription, and cell cycle regulation. Its overexpression has been detected and related to many types of cancers including leukemia, suggesting that suppression of cyclin A2 would be an attractive strategy to prevent tumor progression. Herein, we apply functionalized single wall carbon nanotubes (f-SWNTs) to carry small interfering RNA (siRNA) into K562 cells and determine whether inhibition of cyclin A2 would be a potential therapeutic target for chronic myelogenous leukemia. The results show functionalized SWNTs can facilitate the coupling of siRNA specifically targeting human cyclin A2 to form cyclin A2 siRNA–f-SWNTs complexes. These functionalized SWNTs readily enter K562 cells, resulting in suppression of cyclin A2 expression. We demonstrate that depletion of cyclin A2 in this manner inhibits cell proliferation and promotes apoptosis, and cyclin A2 can serve as a novel therapeutic target. siRNA against cyclin A2 delivered by functionalized single wall carbon nanotubes may be a useful therapeutic strategy for chronic myelogenous leukemia cells. This would provide new insights on additional therapeutic options for chronic myelogenous leukemia beyond chemotherapy in light of increasing multidrug resistance.