Abstract: To study foe effect and the relationship of queroetin on RNA polymerases and cell cycle in Human leukemia HL-60 cells.Treating of HL-60 cells with 4,20 and 100μmol/L quercetin for 2 days,or wilh 20μmol/L for 1-5 days,the cell cycle were analyzed with flow cytometer.And total RNA polymerases activity and RNA polymerase Ⅱactivity were measured in isolated HL-60 nuclei by nuclear transcription in vitro.After treatment of HL-60 cells with quercetin,total RNA polymerase activity,especially RAN polymerase Ⅱactivity showed inhibitory effects in time-and dose-dependent manner.The cells at G₁,phase increased at the same way.This phenomena revealed that quercetin could arrest cell cycle progression of HL-60 at G₁phase.These observation also suggest that quercetin treatment of HL-60 cells gave the inhibitory effects of total RNA polylnerases activity and especially RNA polymerase Ⅱ activity,is related to the cell increase at G₁phase.It may be one of reason that queroetin could block in G₁ phase of HL-60 cell cycle because of its inhibitory effects on nuclear transcripti-on in vtro,especially on RNA polymelase Ⅱ.