Bone cells are adaptive to surrounding mechanical conditions. Osteoblasts, one of bone cells, have been reported to be sensible to mechanical stimulation and change the generated bone mass. Viscoelastic properties of such cells are predicted to be related to this phenomenon in the view of mechanical dynamics. In order to find the effective stimulation on the bone formation, it is necessary to understand the viscoelastic properties of the cells. Especially in the case of bone cells, it is important to consider their adhesive condition because they attach on surfaces of bone matrices. In this study, we measured tensile, static and dynamic viscoelastic properties of a cultured osteoblast, MC3T3-E1, under adhesive condition. Using these experimental results, we derived a model for viscoelasticity of the cell and identified the value of each element in this model. The cells were seeded on a glass plate in a petri dish. After the cells were cultured for one day and adhered on the glass plate, it was vertically raised and fixed on a piezo actuator. The center of the cell surface was aspirated with an L-shaped micropipette to be held. The glass plate was moved with manual, an electric motor or the piezo actuator according to the types of tests. The load applied to the cell was obtained by measuring the deflection of the micropipette whose spring constant was calibrated after each test. Deflection of the micropipette and elongation of the cell were measured by captured image during the test. As a result, the viscoelasticity of the cells was measured and modeled, and the value of each element in this model was identified.