Objectives Using FX-4000 strain unit,the viscoelasticity of human lung adenocarcinoma A549 cells that underwent mechanical strain of different elongation amplitude were studied.Methods A micropipette aspiration technique was adopted to investigate the viscoelasticity of A549 cells,compared with 15% elongation -treated cells and 1.5% elongation-treated cells.A standard linear solid model was employed to fit the experimental data and three viscoelastic coefficients were used to compare the mechanical properties of control cells,15% elongation-treated cells and 1.5% elongation-treated cells.Results Viscoelastic coefficients k_1,k_2 andμvalue all reduced after A549 cells were subjected to 15% elongation with sine wave at frequency 0.5Hz for 4h compared with the control group,while the viscoelastic coefficients had no distinct difference compared with that in 1.5% elongation -treated cells.Conclusion The deformability increases and the rigidity decreases could be found for 15% elongation-treated cells.Such changes in the viscoelastic properties of cancer cells probably affect tumor cell invasion or metastasis as well as interaction between tumor cells and their micro-mechanical environment.