|Abstract||The natural compound, thymoquinone (TQ) has demonstrated potential anticancer properties in inhibiting cell proliferation and promoting apoptosis in myeloid leukemia cells, breast cancer cells, and others. However, the effect mechanism of TQ on AML cells still not fully understood. In this study, the authors examined the effects of TQ on the expression of JAK/STAT-negative regulator genes SOCS-1, SOCS-3, and SHP-1, and their consequences on cell proliferation and apoptosis in HL60 leukemia cells. MTT and trypan blue exclusion tests were conducted to determine the 50% inhibitory concentration (IC50) and cell proliferation. FITC Annexin and Guava® reagent were used to study the cell apoptosis and examine the cell cycle phases, respectively. The expression of JAK/STAT-negative regulator genes, SOCS-1, SOCS-3, and SHP-1, was investigated using reverse transcriptase- quantitative PCR (RT-qPCR). TQ demonstrated a potential inhibition of HL60 cell proliferation and a significant increase in apoptotic cells in dose and time-dependent manner. TQ significantly induced cycle arrest at G0-G1 phase (P < 0.001) and enhanced the re-expression of JAK/STAT-negative regulator genes. TQ potentially inhibited HL60 cell proliferation and significantly increased apoptosis with re-expression of JAK/STAT-negative regulator genes suggesting that TQ could be a new therapeutic candidate for leukemia therapy.<br />.