Once it is designed, the stiffness of a compliant mechanism is not intended to be changed in order to adapt to special operation conditions. Nevertheless, various operation tasks e.g. mechanical grippers, would benefit from such a feature. The effect of axial compression forces, however, is well known to reduce the transverse stiffness of beam-like structures. This paper deals with the effect of prestressing forces on compliant mechanisms. For this purpose, a mathematical description for a modal analysis of compliant mechanisms — based on the author’s former publications — is presented first. Building on this and using a compliant mechanism with one desired translational motion as example, the effect of prestressing forces on the desired deformation and its related stiffness value is analyzed using conventional methods which are based on the Bernoulli-Euler beam equation. However, these methods do not usually consider the undesirable deformations of a mechanism. The modal analysis mentioned above is therefore used in order to examine the effect of prestressing forces on both the desired and undesired deformations. In this analysis, two different compliant mechanisms in several load cases are examined.