recent years have seen the initial success of the variational implicit-solvent modeling of biomolecules. the dielectric boundary or the solute-solvent interface is the key quantity in such modeling. this work concerns the effective dielectric boundary force that contributes significantly to the conformation and dynamics of an underlying biomolecular system. such a force is the "normal velocity" in the level-set numerical computation of equilibrium biomolecular structures. precisely, the dielectric boundary force is defined as the shape derivative of the electrostatic free energy. both the poisson-boltzmann free energy, and its coulomb-field and yukawa-field approximations are considered. analytical formulas of the corresponding dielectric boundary force are derived. this is joint work with hsiao-bing cheng, li-tien cheng, and xiaoliang cheng, and zhengfang zhang.