Gas velocity is a critical operational variable in the electrostatic precipitation process. However, studies concerning the collection of nanoparticles have ignored the effect of low gas velocities. Therefore, the aim of this work was to use a wire-plate electrostatic precipitator to investigate the effects of atypical gas velocities under different electric fields on the efficiency. Increasing of both variables enhanced the efficiency, under the conditions used. Unusual behaviors of the grade efficiency curves were associated with diffusional effects. The experimental overall efficiency data were compared with the Deutsch model, and effective migration velocity curves with maximum points were obtained.