The apparent viscosity of dilute solids suspension flows has been inferred from the experimentally measured frictional pressure drop in a specially designed downflow straight pipeline. The results indicate that the apparent viscosity of gas-solid suspension flow increases with the increment of the solids holdup, and is, in the transition region only, inversely proportional to the gas velocity. As the influence of gas velocity to the gas-solid suspension flow becomes negligible in the turbulent region, the apparent viscosity can be linearly correlated with the solids holdup. New correlations for the apparent viscosity of the gas-solid suspension flow in straight pipelines were proposed. (C) 2019 Elsevier B.V. All rights reserved.