Humidity is one of the most important quantities that should be monitored and controlled in many environments. The applications of humidity measurement range from domestic indoor air quality control to industrial process control.Many humidity dependent physical phenomena have been employed for the fabrication of humidity sensors. Among them are the variation of electrical resistance and capacitance of humidity sensitive materials. High sensitivity, low cost, wide dynamic range and linear response have rendered capacitive humidity sensors the dominant sensor in use today. The basic structure of these sesnors consists of a pourous dielectric that is sandwiched between two conductive electrodes. At least one of the electrodes should be permeable to water vapor. Absorption of water vapour molecules into the porous dielectric changes the dielectric constant and hence the capacitance of the sensor. This project deals with the fabrication, characterization and modeling of Al/Poures Al 2 O 3 /Porous Ag capacitive humidity sensor. Pure sheets of Aluminium were used as the substrates. The surface of the samples was oxidized using electrochemical anodization. Then a porous layer of Ag was deposited on top of the anodized aluminium oxide (AAO) as the second electrode using the drop cast method. The porousity and microstructure of the dielectric and metal electrode was investigated using SEM micrographs. The impedance of the fabricated sensors was tested at 0 to 100% of related humidity (RH). Results of experiments showed that the sensor response considerably changes above 60% RH. Also the response is linear in this range. A simple R-C model was employed to relate the sensor impedance to the electrical properties of the structure. The extracted capacitance component of the impedance was further verified against different adsorption isotherms. The results showed that the water content of the porous alumina closely follows the Frandlitch isotherm. The effect of operating temperature, measurement frequency and anodization time on the sensor response were also studied in this project. Sensor capacitance increased with temperature in the mid RH range. The sensitivity of the sensor was decreased by increasing the measurement frequency. Samples with shorter anodization time showed lower sensitivity to relative humidity. Based on the experimental and theoretical results Al/Poures Al 2 O 3 /Porous Agstructure is a good, reproducible and stable humidity sensor especially at high relative humidities. Also, a key finding of this work is that the drop casted layer of Ag particls can well act as the porous electrode. Keywords: Capacitive Humidity Sensor, Aluminium Anodization, Modeling of Sensor Response.