Flow regimes and their transitions in the gas-liquid-solid mini-fluidized beds (MFBs) with single gas orifice were studied experimentally in this paper. The diameter of the fluidized beds varied from 3 mm to 5 mm and the vertical column height was 50 mm. The ranges of superficial gas velocity and liquid velocity were 1.96 x 10(-4)-4.73 x 10(-3) m/s and 5 x 10(-6)-4.2 x 10(-2) m/s, respectively. The solid particles ranged in size from 50 pm to 300 pm. Half-fluidization, slug, dispersed bubble and transport flow regimes in the three-phase MFBs were identified by analyzing minimum fluidization velocity, pressure drop, and entrainment velocity of solid particles based on experimental data of pressure drop and fluidization velocity as well as flow observations. The effects of solid particle, liquid properties, bed, gas orifice sizes, and static bed height on the flow regimes and transitions were investigated. Results showed that the behavior of gas bubbles and the wall effect affected the flow regimes and transitions. Obvious wall effect increased minimum fluidization liquid velocity in the liquid-solid mini-fluidized beds, which increased the transition liquid velocity from the half-fluidization to slug flow regimes. Moreover, wall effect made Taylor bubbles bigger at lower superficial liquid velocities due to the bubble coalescence and the transition boundaries expansion. Solid particles aggregation, wall effect and bubble wake behavior were responsible for increment of the minimum entrainment velocity of solid particles. Flow regime maps of the gas-liquid-solid MFBs were presented and correlations were suggested for the flow regime boundaries. (C) 2018 Elsevier B.V. All rights reserved.