The effects of milling time on the rheological behavior of 70-vol% loaded fused silica slurries were studied. A transition from shear thickening to shear thinning behavior was observed with milling time. Slurry viscosity and thixotropy attained a minimum after 18 h of milling and remained almost unchanged with additional milling. Infrared spectroscopy and particle surface charge measurements confirmed the development of increasing amount of surface hydroxide and surface charge respectively with progress in milling time, leading to shear thinning behavior. An initial static aging treatment of 24 h aided the development of silanol groups, indicating that the milling time can be reduced to save energy and time.