After analysing the characteristics of the breakage distribution parameter [P.B. Rajendran Nair, Breakage parameters and the operating variables of a circular fluid energy mill: Part I. Breakage distribution parameter, Powder Technol. (1999) accepted], the next parameter of importance in the context of modeling and simulation of the process of grinding in a circular fluid energy mill is the breakage rate inside the grinding chamber. Using the G-H solution for the size discretised batch grinding equation and a back-calculation scheme, the breakage rates for different grinding chamber conditions of the circular fluid energy mill, with respect to the grinding nozzle pressure, nozzle size and material feed rate were estimated. The breakage rate parameters of different particle sizes, for a given grinding condition, could be related to the rate of disappearance of the top size interval by a power function of the dimensionless particle size, but with broken lines, one to represent the coarser size fractions and the other for the finer size fractions. The coefficients of these power functions were characterised with the operating variables of the mill with appropriate relations.