Pyrolytic gasification of polyethylene (HDPE) by partial combustion is carried out in a porous alumina fluidized bed 57.5 mm in diameter and 600 mm in length for the purpose of reusing plastic wastes. Attainment of steady state is confirmed under conditions of 30 to 240 min of feedtime of HDPE. Operating conditions, such as feed rate of HDPE and amount of alumina for efficient gasification, are studied experimentally. Gasification by a porous alumina fluidized bed is characterized by cleanliness due to less formation of soot. The real-time measuring of pressure drop through the fluidized bed is found to be practical to confirm attaining the steady state because when pressure drop through the fluidized bed becomes constant, the mass balance of carbon is closed. Although the bed temperature is constant within 30 min., the runs are non-stationary since pressure drop through the fluidized bed continues to increase. It seems likely that some carbonaceous substances occupy the porous portion of the alumina in the steady state of this gasification operation. The optimum condition to give both a product gas of high lower heat value and a tolerable amount of oil and char is found to be an air ratio of 0.2 to 0.3 and a bed height/column diameter ratio of 1.0 to 1.5.