The profile of pressure difference and mixing degree were investigated with binary system of different density using PMMA(poly methyl methacrylate) and sand(or manganese ore) in a 0.109 m I.D. gas fluidized bed. This study is carried out the systems jetsam rich system and flotsam rich system. A study on mixing-segregation phenomena was performed by the analysis of the profile of pressure difference, and the results were confirmed with mixing degree using sieve test. It was found that the take-over velocity was obtained from the value of specific gas-velocity which observed by transition of the slope in a pressure differences profile. The mixing degree is related with variation of the bed pressure difference measuring height of axial position according to gas velocity.