Among environmental issues affecting cultural relics, art objects and documentation materials, low concentrations of the pollutant, formaldehyde, have a great potential for causing damage. In the presence of light and heat, formaldehyde may form complex substances which may cause even more damage. There is little research on the effect of formaldehyde on different categories of cultural relics. In the present study, different concentration of formaldehyde in micro-environments were tested using a quartz crystal film electrode (the composite electrode) modified with polyaniline in conjunction with a quartz crystal microbalance (QCM). The results showed the composite electrode responds well to the formaldehyde. The frequency change of the composite electrode shows a direct relationship with time. Moreover, as the concentration of formaldehyde increases, the change in frequency of the composite electrode and the speed decreases. The study also indicates that there is a linear correlation between the concentration of formaldehyde and change in frequency of the composite electrode. Therefore, the concentration of formaldehyde could be deduced from experimental results. This method provides a means for real-time monitoring of the concentration of formaldehyde and represents way to evaluate the storage environment of cultural relics.