Quercetin (QU) and trichostatin A (TSA) are promising anticancer drugs. While QU mainly exerts its anticancer activity through scavenging reactive oxygen species (ROS), the anticancer activity of TSA was attributed to its inhibition on histone deacetylases (HDAC). In the present study it was investigated, whether the combination of QU and TSA could improve their anticancer activity against human leukemia cells (HL-60). The cytotoxicity of QU and TSA increased in a time and dose-dependent manner. QU (10, 20 and 40 microM) was able to diminish the ROS generation (indicated by the level of malondialdehyde, MDA) but showed no influence on the histone acetylation in HL-60 cells; on the contrary, TSA (20, 40, 80 and 160 nM) showed no inhibition on ROS generation but significantly increased the histone acetylation, indicating the possible role of both scavenging ROS and increasing histone acetylation in the induction of cell death in HL-60 cells. This conclusion was confirmed by the findings that the combinations of QU and TSA at different concentrations could not only diminish ROS generation, but also increase histone acetylation, and hence showed more significant cytotoxicity in HL-60 cells than either of its components. Collectively, the present data indicate that a combination of QU and TSA can cooperatively kill HL-60 cells through the combination of their activities of scavenging ROS and increasing histone acetylation.