We apply dielectrophoresis to separation of cells in a culture broth by considering the difference of dielectric constant between alive and dead cells. In this paper, the dependency of the apl,lied a-c voltage' s frequency on the dielectrophoresis for yeast, E-coli, animal cells is studied and the method of cell collection is also discussed. A suspension of cells was filled into well mounted pin-plate electrodes and well mounted wire-cylinder electrodes, and an a-c voltage was applied between the electrodes. The ranges of the electric field strength and the frequency were from 2X10(3) V/m to 1x10(5) V/m and from 1 kHz to 1 MHz, respectively. Three kinds of alive cells can be collected at a frequency of 1 MHz, and the dead cells can never be collected at this frequency. At that time, there was no detrimental effect, even when applying the a-c electric field of 1x10(5) V/m to alive cells. The collection rate of alive cells is greatly influenced by the electric conductivity of the culture broth. The optimum electric conductivity for the collection rate of alive cells is 100 muS/cm.