Polymerase chain reaction (PCR) is one of the most sensitive and specific detection methods of bacterial and viral infections. The authors proposed a new electrical technique for rapid detection of DNA amplified by PCR using dielectrophoresis (DEP) of microbeads. The method is based on dramatic alteration of DEP characteristics of microbeads caused by DNA labelling. DNA labeled microbeads are trapped on a microelectrode under the action of positive DEP, whereas pristine microbeads are not. DEP-trapped microbeads can be measured impedimetrically to realize rapid and quantitative detection of the amplified DNA. In this study, it was aimed to reveal how DNA length affects DEP characteristic of DNA-labeled microbeads. Dielectrophoretic crossover from the negative to the positive was measured for microbeads labeled with DNA length in 204 bp, 391 bp and 796 bp. After theoretical fitting of DEP crossover data, it was revealed that the surface conductance increased when the length of labeled DNA increased.