Owing to the outstanding dielectric properties derived from the conjugated π-electron systems, conjugated polymers have been explored and developed in capacitive humidity sensors for a few decades. In this work, a series of composites – mesoporous silica and semiconducting polymers – MCM-41 (MCM, Mesoporous Crystalline Material)/PEDOT (poly(3,4-ethylenedioxythiophene)) were chemically obtained by in-situ polymerization at 0 °C, while the amounts of PEDOT were adjusted by different evaporation times of EDOT (3,4-ethylenedioxythiophene) in the porous MCM-41 film. Additionally, it was able to modulate both the dielectricity and porosity of the composites via this convenient approach. The obtained capacitive humidity sensors based on MCM-41/PEDOT composites exhibit much better sensing performance than their bulk counterparts, with wider humidity sensing range, higher sensitivity and much faster response speed.