Organic–inorganic hybrids have drawn great attention for gas sensors due to their high sensitivity, good selectivity and acceptable stability at room temperature. There are two main approaches by which organic–inorganic hybrids convert gas information to electric or optical signals (vapochromism). Here, we have reported a new organic–inorganic hybrid PEA₂MnBr₄ for humidity detection by luminescent visible chromism. PEA₂MnBr₄ single crystals were grown by the solution method and determined by single-crystal X-ray diffraction. Luminescent humidity chromism was found on PEA₂MnBr₄ from green emission at the water-desorption state to pink emission at the water-adsorption state within 18 s at a relative humidity of 38% RH. This obviously visible chromism was further used to check the water content in toluene with a low detection limit between 0.02 and 0.05 vol%.