A microporous organic polymer based on 1,3,5-trihydroxybenzene was synthesized, and the structure and properties of the resultant polymeric organic framework (POF) were determined by a series of characterizations. The POF acted as a host to load different amounts of LiCl for the preparation of humidity sensitive materials. Compared with the pure POF sensor, the LiCl/POF sensors showed improved humidity sensitive properties, especially the 4 wt% LiCl/POF sensor. The impedance of the optimum sensor changed by three orders of magnitude, with good linearity over the whole humidity range. Moreover, the optimum sensor showed little hysteresis, good long-term stability and a rapid response time. In order to explore the conductive mechanism, the complex impedance plots of the optimum sensor were discussed.