A semi-empirical model was proposed to estimate the apparent viscosity of gas-fluidized suspensions. This new model was derived by assuming that a suspension consisted of the bubble phase and the emulsion phase. A set of experimental measurements were also conducted to verify the validity of the proposed model as well as the models in the literature. The results indicated that none of the tested literature models provided satisfactory predictions for the fluidized gas-solid suspension over the mentioned target particle volume fraction range. The estimation using the newly proposed model generally well agreed with the experimental apparent viscosity values of the gas-solid suspensions composed of gas-fluidized Geldart Group A or B particles, as most of the estimated values situated within the 25% error bars. The proposed model is of special significance as it provides a quick estimation method of the apparent viscosity of a gas-solid suspension flow in the engineering calculation. (C) 2020 Elsevier B.V. All rights reserved.