In this work, highly sensitive low-humidity sensors based on Au nanoparticles (NPs)-modified sulfonate metal–organic frameworks (MOFs) were constructed, and the sensor was applied in low-humidity detection. Small Au NPs can enhance the hydrophilicity of the sensing material and catalyze the decomposition of water molecules, and the generated protons can be conducted through the sulfonate group. The as-obtained optimum low-humidity sensor constructed with small Au NPs (   ≈2   nm)-modified MOFs exhibits a response of 904% with good linearity in the humidity range of 5% RH–30% RH. The as-prepared sensor with high sensitivity and good long-term stability was applied in biscuits storage environment monitoring. This work provides a promising material for preparing highly sensitive low-humidity sensors.