Resistive type relative humidity sensors based on CdS nanoparticles were synthesized using the chemical bath deposition (CBD) method. Using the drop-casting method, CdS nanoparticles were deposited between thermally evaporated gold electrodes separated by 17 mu m with the electrodes having channel widths of 1400 mu m and supported on a glass substrate with a thickness of 120 nm. The CdS nanoparticles were exposed to moisture to measure the change in electrical resistance. The resistance of the CdS sensor element changed by 3 orders of magnitude as the relative humidity of the test cell was varied between 17 and 85%. The experimental results demonstrate that CdS nanoparticles are very sensitive to changes in relative humidity and can be used as a sensing element for CdS-based humidity sensor applications.