The stability of a magnetically stabilised fluidised bed (MSFB) has been studied in an experimental investigation coupled with mathematical modelling. Experimental results indicate that the stability of the bed can be influenced by several factors, including liquid velocity, magnetic field strength, solid and liquid density, solid magnetic susceptibility and solid particle size distributions. A theoretical model based on Rosensweig's mean field theory and the Richardson-Zaki equation has been established to predict the bed transition velocity when a fluidised bed starts to transform from a stable to an unstable state against an applied induction. The model predictions were found to have reasonable agreement with the experimental values obtained from bed pressure drop measurements. The results have applications to the design of magnetically stabilised fluidised bed bioreactors.