The initial fluidization characteristics of gas-liquid-solid minifluidized beds (MFBs) were experimentally investigated based on the analyses of bed pressure drop and visual observations. The results show that ULmf in 3-5 mm MFBs can not be determined due to the extensive pressure drop fluctuations resulting from complex bubble behavior. For 8-10 mm MFBs, ULmf can be confirmed from both datum analyses of pressure drop and Hurst exponent at low superficial gas velocity. But at high superficial gas velocity, ULmf was not obtained because the turning point at which the flow regime changes from the packed bed to the fluidized bed disappeared, and the bed was in a half fluidization state. Complex bubble growth behavior resulting from the effect of properties of gas-liquid mixture and bed walls plays an important role in the fluidization of solid particles and leads to the reduction of ULmf. An empirical correlation was suggested to predict ULmf in MFBs. (C) 2016 American Institute of Chemical Engineers