We have examined the induction of HL-60 cell differentiation by treatment of the water extract of Rhizoma Zingiberis Siccatum, which is a Korean traditional herbal medicine. It was observed that HL-60 cell proliferation was dose-dependently inhibited by treatment with various dose of Rhizoma Zingiberis Siccatum extract. The level of inhibition was identical to those of ATRA-treated cells. Rhizoma Zingiberis Siccatum extract treatment caused a significant change in NBT reduction (47%) and enhanced ATRA-induced NBT reduction. Treatment of Rhizoma Zingiberis Siccatum to HL-60 cells increased only CD11 b expression in the cells, and also increased markedly G0/G1 stage arrest. This can suggest that Rhizoma Zingiberis Siccatum induced the differentiation of HL-60 cell and enhanced ATRA-induced differentiation predominantly along the granulocytic lineage. The results present here show that Rhizoma Zingiberis Siccatum extract contains the potential effect of differentiation induction or acts as a agent enhancing the induction of differentiation.