Composites with embedded SMA wires as actuators work as solid-state actuators, and are therefore able to control the shape of a structure without requiring moveable parts. An important aspect to compare the behaviour and efficiency of such active structures as a function of size is scalability. In this framework it is very important to qualify the interface between SMA wires and matrix. An investigation on scalability of SMA composites by roughness evaluation of SMA wires is presented in this paper. The authors measured roughness of thin Ni-Ti wires with different diameters (0.05 mm, 0.075 mm and 0.1 mm) by processing SEM (Scanning Electron Microscopy) photography with a special software package. During SEM photography of SMA wires, in the vacuum room of SEM microscope a relevant part of the electron beam emission is transformed in heat.