We have systematically investigated the real-time I-DS responses and electrical characteristics of pentacene OTFTs exposed to six volatile compound vapor flows of acetone, ethanol, methanol, water, chloroform, and toluene, which could be classified into two group according to the influence on the electric performance of OTFTs. The first three compounds caused remarkable and irreversible degradation of electric performance of OTFTs. However, the latter three compounds caused slight and reversible changes of their electric performance. Moreover, the good linearity existed in plot of changes of the normalized IDS as a function of their concentrations in N-2 flow.