In this paper, a low-cost capacitive relative humidity hygrometer suitable for food moisture monitoring is presented. The variation of dielectric constant of polyimide film to relative humidity enables the sensor's functionality. A fully differential capacitance to digital converter is utilized as the hygrometer digital readout, which is immune to circuit wiring parasitic and enable the sensor's long-term stability. The humidity sensor is implemented using TSMC1P6M 0.18μm technology with thick top metal option. Simulation results indicate that an inaccuracy of +6/-5%RH can be achieved sensing from 10%RH ∼ 90%RH, with 5.4μW power consumption for sensing and 21.6mW power consumption for sensor heating.