A new two-step amplifying mechanism combining a lever-arm with flexure hinges and a pre-curved thin shell structure is proposed to make a millimeter-scale linear actuator. A large amplification ratio can be obtained by the snap-through effect of a post-buckled shell structure without losing actuation force. The snap-through phenomenon of pre-curved thin-plate are numerically analyzed by using the finite-element software ABAQUS to specify the trigger force and displacement required to initiate the snap-through. The analytic results are in good agreement with the test results for the pre-curved shell structure. The trigger force and displacement for snap-through are supplied by the lever-arm with the piezo stack actuator. Amplification ratio of the lever-arm is drastically changed according to the external load. The lever-arm mechanism is designed to have enough actuation force and displacement to satisfy requirements such as trigger force and displacement of the bi-stable structure. The components of the designed actuators are manufactured and integrated. The designed two-step amplified actuator is experimentally validated to operate with an 8 mm stroke and 2 Hz bandwidth. (C) 2013 Elsevier Masson SAS. All rights reserved.