Accurate mass flow rate measurement of multiphase flows is a major challenge in the process industry. In this paper, a microwave tomography sensor for the concentration measurement and a microwave Doppler sensor for the velocity measurement are presented for the determination of mass flow rate of gas-solid flows in a pipeline. The method of approach including data acquisition, image reconstruction and short-time FFT is described. With the technique, the concentration of bulk solids in the flow is measured and visualized using the microwave tomography sensor. Based on the velocity and concentration of bulk solids, a time varying mass flow rate can be calculated. The experimental study shows that the mass flow rates measured with the microwave sensors agree well with their actual values. The test results are also presented. (C) 2019 Elsevier B.V. All rights reserved.