Innovative research progress has been made recently by Professor Zhao Yapu’s research team entitled “NEMS/MEMS Mechanics and Physical Mechanics” in studying the influence of surface forces on nanoelectromechanical systems (NEMS). The influence of van der Waals (vdW) and Casimir forces on the stability of the electrostatic torsional NEMS actuators is analyzed in this paper. With the consideration of vdW and Casimir effects, the dependence of the critical tilting angle and pull-in voltage on the sizes of structure is investigated. And the influence of vdW torque is compared with that of Casimir torque. The modified coefficients of vdW and Casimir torques on the pull-in voltage are, respectively, calculated. When the gap is sufficiently small, pull-in can still take place with arbitrary small angle perturbation because of the action of vdW and Casimir torques even if there is not electrostatic torque. And the critical pull-in gaps for two cases are, respectively, derived. This paper has been published in the latest issue of Journal of Microelectromechanical Systems 13(6): 1027-1035 (2004). This journal has been recognized as the top international journal in the filed of MEMS worldwide.