Immature colon carcinoma transcript 1 (ICT1), a human mitochondrial translation release factor, is a ribosome-dependent codon-independent peptidyl-tRNA hydrolase. ICT1-deficiency has been recognized as a cell growth inhibitor of hepatoblastoma and glioblastoma multiforme. To explore the role of ICT1 in human leukemia, 2 short hairpin RNAs (shRNAs) targeting ICT1 sequences were designed in leukemia U937 cells. The successful infection of ICT1 in the U937 cells was observed under a fluorescence microscope and further quantified by western blotting and quantitative real-time PCR (qRT-PCR) analysis. Tetrazolium dye (MTT) assay revealed a significant decrease in proliferation of ICT1-knockdown U937 cells on the fourth and fifth day as compared with the control. Depletion of ICT1 resulted in an increase in S phase and sub-G1 (representing cell apoptosis) fractions. Annexin V-APC/7-AAD staining assay confirmed that knockdown of ICT1 played a crucial role in boosting early and late apoptotic programs in U937 cells. Downregulation of ICT1 also altered cyclin A2 transcription expression, caspase-3 activity and p21 protein expression. Additionally, decreased levels of heat shock protein 27 (HSP27) phosphorylation at Ser78 was correlated with knockdown of ICT1 in U937 cells. Thus, we concluded that the regulatory role of ICT1 in leukemia may be used as a potential therapeutic target for the treatment of leukemia.