The influence of the properties of a slurry on the flocculation behaviour of fine particles in water upon the application of a DC electric field was investigated. In addition, the mechanism whereby particles in water can be flocculated through the application of the DC electric field was clarified. The particle flocculation efficiency was determined for aqueous and non-aqueous slurries to which a DC electric field was applied, by measuring the change in the turbidity of the sampled slurry. It is shown that, for aqueous slurries, the particle flocculation could be enhanced by applying a DC electric field provided the particles carried a charge and were surrounded by an electric double layer. It was also found that there was no enhancement of the flocculation for those slurries for which pH = pH(IEP), as well as for nonaqueous slurries using rapeseed oil as their solvent, in which case the particles were not charged. In addition, merely stirring the slurry (thus increasing the number of particle collisions) did not cause the particles to flocculate, although the particle flocculation could be enhanced by applying a DC electric field while stirring the slurry, thus maintaining a constant particle concentration. These findings lead to the conclusion that the enhancement of the particle flocculation in an aqueous slurry through the application of a DC electric field is caused by the charged particles and their counter ions in an electric double layer forming an electric dipole due to the deformation of the electric double layer, thus creating an electrostatic attractive force between the particles.