The characteristics of an internal slurry were analyzed during ball milling, which is commonly utilized in ceramic processing. We used a device with a capacity of 50 L because this is the size employed in industries, and built a circulation system to collect the slurry during the milling process. The properties of the slurry were characterized in terms of their particle size and viscosity, while vibration data were collected from the side of the ball mill drum in real time. A fast Fourier transform was performed on the vibration data, allowing the energy to be calculated and compared with the slurry characteristics. The vibration data in the 3-4 kHz range showed a strong negative correlation with the slurry viscosity. Our results con rm that the characteristics of the internal slurry can be monitored in real time using vibration data collected during ball milling.