Due to historical reasons and significant medical potential, the importance of mechanical environment on the functioning/fate of cells is becoming very well recognized in animal cell biology, and also for bacterial cells. The least documented are the mechanobiological phenomena in plant cells and plants themselves[1] even though the three major challenges for humankind in the 21st century are food, energy, and the environment; where plant life plays an essential role in all these. The presence of the plant cell wall certainly poses conceptual challenges for the application of techniques such as atomic force microscopy directed at the cytoskeletal elements [2]. Here we circumvent the interference by the cell wall via study of the protoplasts using quartz crystal microbalance (QCM), a technique we previously used for the study of cell adhesion and viscoelastic properties of animal cells [3], for the study of viscoelastic properties of protoplasts extracted from Columbia wild Arabidopsis leaf. Arabidopsis protoplasts were immobilized on the poly(diallyl dimethyl ammonium chloride) (PDADMAC)/SiO2 QCM electrode via the electrostatic adsorption between negatively charged protoplasts and positively charged PDADMAC. The QCM frequency shift and motional resistance change verified the viscoelastic properties of the immobilized protoplasts. The protoplasts under isotonic pressure (about 0.3 M mannitol) were subjected to hypertonic and hypotonic treatments and the viscoelastic changes accompanied were monitored continuously with the QCM technique. The QCM results were discussed along with the simulation results from the morphological changes of the protoplasts immobilized onto glass slides observed by an optical microscopy.