In this study, mixing of fine powders with flammable insulator liquid was conducted and continuous monitoring of the static electrification during the mixing operation was attempted by a Faraday cage and a newly developed electrostatic field sensor. The effects of operating parameters (agitation speed, particle size, powder concentration) on the electrification were investigated experimentally. The experimental results implied that the electrification increased with an increase in agitation speed and a decrease in particle size. The electrification also increased when the powder concentration increased, however, too much powder concentration greater than 30 wt% could not increase the electrification further. The electrification during mixing was also measured under various vessel sizes and the scale-up characteristics was analyzed by means of agitation power per unit volume, blade tip speed and slurry circulation velocity. It was found that the scale-up of electrification during solid mixing was well conducted by means of agitation power.