CD24 has been reported to have a role in metastasis of several malignancies including breast cancer. We investigated the effect of CD24 expression on biologic features in human breast cancer cells, and found that CD24 expression is associated with more rapid growth and enhanced ability of adhesion and invasion in MCF-7. The proportion of cells was higher in synthetic phase and lower in arrestic phase for CD24high than for CD24low/- cells. Cyclin D1 and p27 had stronger expressions in CD24low/- cells than CD24high cells. These suggested one possible pathway for CD24 effect on proliferation.