Abstract: Investigates the effect of ball milling parameters on the particle size of powdered NiFe2O4 spinel. Based on the ball size that was calculated to meet the requirement for lab test, a series of orthogonal tests were carried out to select parameters appropriate to the ball milling process. Test results showed that the duration of ball milling process is the predominant factor to the particle size, and the ball size grading also has an important effect on the distribution range of particle size. A set of optimum parameters for such a ball milling process is thus recommended as follows. Time required for ball milling: 36 h; ball size grading: 35:40:25; mass ratio of the stuff to mill to the ball: 1:2; and the volumetric percent of water contained in slurry: 75%.