A method to enhance microwave tomography through the use of an inhomogeneous background is proposed. Here, the measurement region is located in a circular perfect electrical conductor (PEC) chamber where known objects are placed inside the imaging domain as an inhomogeneous background. The Green function of a circular PEC chamber with inhomogeneous background is obtained using the method of moments. Inversion results obtained with both homogeneous and inhomogeneous backgrounds; then they were compared and discussed. Synthetic studies show that the use of inhomogeneous background can improve the resolution. This method can enhance the inversion results without changing the microwave tomography system.