The new incidence of breast cancer ranks the first in the incidence of female malignant tumors. It is urgent to develop new diagnosis and treatment methods. In vitro cell experiments, liquid media were needed, and the three commonly used media are PBS, DMEM culture medium and DMEM+10% Fetal Bovine Serum (FBS) culture medium. However, the effect of liquid medium environment on the mechanical properties of breast cancer cells is rarely reported. Using atomic force microscope (AFM), we measured the elastic modulus of breast cancer cells in the above three kinds of liquid medium environment. The elastic modulus are 2586.91±663.45 Pa, 2106.86±692.07 Pa and 1586.52±794.01 Pa. The elastic modulus in PBS is 1.63 folds of that in DMEM+10%FBS, a difference close to that of healthy and cancerous breast cells in the same liquid medium. The cell adhesion force to AFM probes in the above three liquid media environments are 63.81±24.50 pN, 66.09±26.41 pN and 121.97±43.99 pN, respectively. Cell adhesion force in DMEM+10%FBS medium is significantly different from that of the other two liquid media.