This article evaluates the effects of operating parameters on fine particle grinding process with a vertically stirred media mill. The effects are investigated through size reduction under different operating conditions by changing solids content, tip speed and the configuration of the impeller. Solids content at 65% (w/w) is demonstrated to be more efficient than 75% (w/w). The maximum difference in product size (D-80) is about 2 mu m. Velocity maps are described at tip speeds of 5.23 m/s, 6.54 m/s and 9.81 m/s by positron emission particle tracking (PEPT). The lower tip speed saves the specific energy 50-100 kWh/t. Over energy input 100-300 kWh/t, D-80 of product is reduced 1-2 mu m by replacing standard impeller with new types of impeller.