MIL-100(Fe) with good hydrothermal stability and high hydrophilicity is considered to be a potential adsorbent for adsorption heat pumps (AHPs). However, its water vapor adsorption performance at low relative humidity needs to be improved. In this study, composite adsorbent LiCl@MIL-100(Fe) was synthesized by impregnating LiCl aqueous solution in MIL-100(Fe). The effects of the LiCl loading in the composite on the crystal structure, morphology, composition, pore structure as well as the vapor adsorption/desorption performance of the composites were carefully studied. The results showed that on the premise of ensuring no leakage, the LiCl loading in the composite was up to 32.9 wt%. At 20% relative humidity (RH), the saturated adsorption ratio of the composite (0.260 g/g) was higher than that of original MIL-100(Fe) (0.054 g/g). Meanwhile, the water adsorption rate of the new composite adsorbent was faster than pristine MIL-100(Fe). Moreover, after 50 cycles of vapor adsorption/desorption, the composite adsorbent showed a satisfactory stability. All these indicate that the new LiCl@MIL-100 (Fe) composite adsorbent will be a prospective candidate for high-efficiency AHPs.