This study is to investigate the effect of downregulation histone deacetylases1 (HDAC1) gene by the technology of RNA interference on the differentiation of HL-60 cells line.  The optimal segment targeting HDAC1 gene was designed and transfected into HL-60 cells by Lipofectamine^TM 2000.  The HDAC1 mRNA and protein level were detected by RT-PCR and Western blotting.  The morphologic change of HL-60 cells was detected by an optical microscope with Wright-Giemsa.  Cell differentiation was tested by NBT reduction assay.  Expression of CD13, CD33 and CD14 was measured by flow cytometry.  The results indicated that HDAC1 mRNA and protein were markedly suppressed by the siRNA targeting HDAC1 in a concentration-dependent manner.  HDAC1 siRNA promoted cell differentiation.  HL-60 cells became more mature in morphology after transfected to HDAC1 siRNA at a concentration of 30−60 nmol·L⁻¹ for 24 h.  NBT reduction ability of HDAC1 siRNA with 30 nmol·L⁻¹ was 0.31 ± 0.09, compared with negative control (0.20 ± 0.02) (t = −3.1, P < 0.01), and with 60 nmol·L⁻¹ was 0.25 ± 0.02 in comparison with negative control (0.21 ± 0.04) (t = −2.12, P < 0.05).  But it has no change in HDAC1 siRNA ≥ 120 nmol·L⁻¹.  After transfection with 60 nmol·L⁻¹ HDAC1 siRNA to HL-60 cells, the expression of CD13 was (96.50 ± 0.70)% in compared to siRNA-NC (3.39 ± 0.68) % (t = 164.9, P < 0.000 5), CD33 was (66.73 ± 0.50) % in compared to siRNA-NC (96.80 ± 1.70) % (t = 43.4, P < 0.000 5).  CD14 was (0.53 ± 0.00) % by comparison with siRNA-NC (0.49 ± 0.02) % (t = −0.97, P > 0.1).  HDAC1 siRNA promoted cell differentiation in indicated concentration.  HDAC1 might be one of the targets of gene therapy for leukemia.  Yet the mechanism needs to be further studied.