Organic acid gases with strong corrosive will cause severe damage to a variety of materials, especially to the cultural relics which have great historical value. 1 Hexyl 3 methylimidazolium chloride (C6mimCl) was employed as sensing material coated on quartz crystal microbalance (QCM) for the detection of organic vapors (formic acid and acetic acid). Results indicated that the C6mimCl/QCM sensor showed fast response, excellent sensitivity and good reproducibility towards organic acids. In addition, there was a good linear relationship between the frequency response and the testing concentrations of these organic acid vapors. C6mimCl/QCM sensor could be a good candidate for the real time detection of organic acid vapors in antique conservation environment.