Experimental and theoretical investigations were conducted with regard to the effects of a dielectric material on freeze drying with microwave heating. The experimental results show that the dielectric material can effectively enhance the microwave freeze drying process, and substantial drying time can be saved compared with conventional freeze drying under the operating conditions tested. Theoretical study was performed by numerically solving a heat and mass transfer model of freeze drying with hygroscopic effect using the finite difference method with a moving boundary. The simulation results demonstrate the effectiveness of using the dielectric material in microwave freeze drying, especially when the solid content of the solution to be freeze dried is very low or the solid product has a very small loss factor. Comparisons of the drying curves display good agreements between experimental measurements and model predictions. Based on the profiles of the ice saturation and temperature, mechanisms of heat and mass transfer inside the material were analyzed, and the drying rate-controlling factor was discussed. (c) 2007 American Institute of Chemical Engineers AIChE J, 53: 3077-3088,2007.