In micro-manipulation, the influence of gravitational force becomes extremely small. The adhesional force is more significant for smaller objects. An adhered object can be detached by electrostatic interaction. The electrostatic force generated by the applied voltage and the voltage required for detachment are theoretically analyzed by using the boundary element method (BEM). The system consists of a manipulation probe, a spherical micro-object, and a substrate plate. These object are all conductive. In this study, the voltage for detachment of micro-sphere with 30 /spl mu/m diameter was experimentally clarified, and was compared with the voltage predicted by the BEM analysis. This result gives us the knowledge about the strategy for reliable electrostatic micro-manipulation.