Lidamycin (LDM)iS a member of the enediyne antibiotic family. lt is undergoing phase l clinical trials in China as a potential chemotherapeutic agent. In the present study. We investigated the mechanism by which LDM induced cell cycle arrest in human breast cancer cells. The results showed that LDM induced G1 arrest in p53 wild-type MCF-7 cells at lOW cOncentrations, and caused both G1 and G2/M arrests at higher concentratiOns. In contrast. LDM induced only G2/M arrest in p53-mutant MCF-7/DoX cells. Western blotting analysis indicated that LDM-induced G1 and G2/M arrests in MCF-7 cells were associated with an increase of p53 and p21, and a decrease of phOsphorylated retinoblastoma tumor suppressor protein, cyclin-dependent kinase(Cdk). Cdc2 and cyclin B1 protein levels. However, LDM-induced G2/M arrest in MCF-7/DOX cells was correlated with the reduction of cyclin B1 expression. Further study indicated that the downregulation of cyclin B1 bV LDM in MCF-7 cells was associated with decreasing cyclin B1 mRNA levels and promoting protein degradation, whereas it was only due to inducing cyclin B1 protein degradation in MCF-7/DOX cells. In addition. activation of checkpoint kinases Chkl Or Chk2 maybe contributed to LDM-induced cell cycle arrest. Taken together,we provide the first evidence that LDM induces different cell cycle arrests in human breast cancer cells. which are dependent on drug concentration and p53 status. These findings are helpfuI in understanding the molecular anti-cancer mechanisms of LDM and support its clinical trials