A study was conducted to investigate the size reduction characteristics of rice husk in a batch ball mill. The most popular population balance model was chosen for the analysis. The model parameters are the breakage distribution function () and breakage rate function (). Experiments are conducted with three different feed sizes of rice husk at three different ball charges. From the experimental data, the best fitting breakage distribution function parameter is found. The breakage rate function parameters with process variables such as feed size, ball charge were calculated. The best correlation for the parameter with process variables was obtained by multiple linear regression analysis. Additional experiments were also conducted at different process conditions to verify the correlation. The accuracy of the correlation is also verified for pet coke data of Ray (2000). The correlation describes the experimental data with acceptable accuracy for rice husk and also for pet coke data within the range of process variables studied in this investigation. The calculated values of the breakage rate obtained through the developed correlations have been compared with the respective experimental values with root mean square error of 1.25% and correlation coefficient of 0.95. It is also found that the calculated values agree well with the experimental values.