This paper presents an overview of a new type of thermal micro-actuators using thermally expandable polymers with embedded skeletons. Embedding a stiff skeleton enhances the actuation capability of the thermally expandable polymer. Consequently, the skeleton-reinforced polymers feature a large maximum actuation stress (often above 100 MPa) and a moderate maximum strain (often above 1%) besides a faster thermal response. In addition, the present composite design has room for performance improvement by tuning the volume fraction of the polymeric expander or selecting a proper expander material. Furthermore, the micro-actuators can be taylored for different motion characteristics, using various skeleton shapes. Finally, we discussed the possible applications using the present actuators.