This experimental investigation focuses on carefully determining the drag coefficient of single spherical particles with considerable small diameters in non-stationary motion. A low-speed wind tunnel and a set of high-speed photography system are employed to confirm the displacement of each particle from its trajectory. Moreover, spherical particles of two different densities are used and the minimum diameter of these particles reaches 0.1 mm. Meanwhile, the Basset force generated from the relative acceleration in the gas-particle flow is calculated approximately. The experimental results show that the maximum proportion of Basset force does not exceed 2.2%. In addition, the relationship of C-D-Re for the experimental data is also determined. This research offers fundamental experimental results for industrial applications and also contributes to the research of non-stationary gas-particle flow. (C) 2014 Elsevier B.V. All rights reserved.