In this work, the polymeric ionic liquid (PIL)/ polybenzimidazole (PBI) composites (PIL/PBIs) based humidity sensors were prepared. The humidity sensing properties of the sensors were controlled by the ratio of PIL and PBI in the sensing films, and the optimized sensor performs a high response of 988.1 in the low humidity range (2%−35% RH). The introduction of PBI into sensing film can guarantee the stability of the humidity sensors. The as-prepared sensor can be utilized to detect the moisture in lubricating oil.