We have developed a monitoring system for evaluating the effect of anticancer agent, such as cisplatin and 5-fluorouracil (5-FU). The system mainly consisted of a quartz crystal microbalance (QCM) and a micro CCD camera that can function in a CO₂ incubator. As the behavior on the resonance frequency (F) - resonance resistance (R) diagram shows the viscoelastic change on the surface of the QCM, the effect of the anticancer agent was evaluated with the F-R diagram and the micro CCD camera, in comparison with the results in the case of general culturing (no anticancer agent injection). During general culturing, the resonance frequency decreased and the resonance resistance increased. This means that the mass loading of a viscous material occurred. Observing with the micro CCD camera, the cells were spread, divided, and the number of the cells increased. On the other hand, when the anticancer agent was injected to the cancer cells, the resonance frequency and the resonance resistance increased gradually. This means the decrement of the mass effect and the increment of the viscosity on the QCM. By observation with the micro CCD camera, the number of the cells did not change. The cells shrinked and changed the shape flat to round by loosing the cell activity.