This paper is concerned with an experimental investigation of an electrostatic liquid filter in which a collector is modelled as a single fibre. The effects of mechanical factors such as flow velocity, electric field strength, relative arrangement of collector fibre to flow, etc., on the deposition quantity of particles are studied. The study has shown that a flow velocity exists which produces a maximum deposition quantity and the value of the velocity varies from one test oil to another. It has been found that the deposition quantity is strongly affected by the relative arrangement of the collector fibre to flow. The study has also shown that the deposition quantity differs considerably according to the relative direction of flow and electric field, especially when particles in the oil are distinctively charged positively or negatively.