The pressure fluctuation properties and mixing degree were investigated with a binary mixture of different density particles using polymethyl methacrylate (PMMA) and sand (or natural manganese ore (NMO)) in a gas fluidized bed. This study was restricted to systems of 50% by volume jetsam, i.e. flotsam rich system. Mixing-segregation phenomena were analyzed by pressure fluctuation properties, and the results were confirmed with the mixing degree using a sieve test. It was found that take-over velocities were obtained from the value of the specific gas velocity which was observed by transition of the slope of the standard deviation of pressure fluctuations. The mixing degree was related to the variation of the bed pressure difference by measuring the height of the axial position according to gas velocity. In addition, take-over velocities could likewise be obtained from a pressure difference profile.