The stability of operation of a perforated plate type suspension bed without downcomer was analyzed experimentally and numerically. The effects of the feed rate, the gas flowrate and the opening ratio and hole dia meter of the perforated plates on the operating stability of the fluidized bed were examined. A full three-dimensional discrete particle simulation method proposed by Tsuji [1993] was performed to study the formation of a stable suspension fluidized bed. The course and behavior of particles that formed a dense and stable fluidized bed are discussed. Both the experimental and simulation results of this study show that the process of forming a suspension bed can be categorized into (i) an induced stage, (ii) a growing stage, and (iii) a stable stage. The velocity of gas through the orifice directly controls the formation of the bed while the solid now rate over a considerable range maintains a balanced hold-up in the suspension bed system without downcomers. The existence of a multiplicity of steady states corresponding to different gas flow rates, for the same feed rate and perforated plate type, was observed. Results show that the design of the plate, the particle feed rate and the gas velocity distribution through the hole affect the stability of the fluidized bed. The simulated results agree qualitatively well with experimental observations.