It is well known that, in the case of traditional spouted bed without a draft-tube, there exists a maximum spoutable bed height, beyond which stable spouting is no longer possible, and also that there is no limitation on the bed height in the case of a spouted bed with a draft-tube. However, to date, there has been no report that a minimum spoutable bed height, or lower limit of the bed height, exists in any type of spouted bed. It was, however, found that (here exists a minimum spoutabe bed height in a screen-bottomed spouted bed. The screen-bottomed spouted bed has a draft-tube, but it has no gas-inlet nozzle or orifice. The gas is fed uniformly over the cross-section of the vessel. When the bed height was less than the minimum spoutable one, the solid particles in the annulus were fluidized and then stable spouting could not be achieved.