To develop a qualitative model for the fluidization characteristics of cohesive iron particles, a systematic investigation was performed focusing attention on the mechanism of defluidization and the particle-to-particle neck growth. The neck growth rate determined by a scanning electron microscope (SEM) agreed fairly well with the prediction by the surface diffusion model. Below 1200 K, cohesion force was successfully explained by the neck growth model with the surface diffusion mechanism. The tensile strength of a neck measured by the diametral compression test was 20 MPa. This value agreed with the one obtained from the bed breaking velocity measurement. Defluidization criterion was discussed based on the balance between bubble buoyancy force and neck force. The prediction was validated experimentally.