In this paper the concept of micro-fluidized beds is introduced. A cylindrical quartz reactor with an internal diameter of only 1 mm is used for process conditions up to Click to view the MathML source and 244 bar. In this way, fast, safe, and inherently cheap experimentation is provided. The process that prompted the present work on miniaturization is gasification of biomass and waste streams in hot compressed water (SCWG). Therefore, water is used as fluidizing agent. Properties of the micro-fluid bed such as the minimum fluidization velocity (Umf), the minimum bubbling velocity (Umb), bed expansion, and identification of the fluidization regime are investigated by visual inspection. It is shown that the micro-fluid bed requires a minimum of twelve particles per reactor diameter in order to mimic homogeneous fluidization at large scale. It is not possible to create bubbling fluidization in the cylindrical micro-fluid beds used. Instead, slugging fluidization is observed for aggregative conditions. Conical shaped micro-reactors are proposed for improved simulation of the bubbling regime. Measured values of Umf and Umb are compared with predictions of dedicated 2D and 3D discrete particle models (DPM) and (semi)-empirical relations. The agreement between the measurements and the model predictions is good and the model supports the concept and development of micro-fluid beds.