This paper is focused on research on research concerning activation time of elements made of Ni-Ti alloy (55/45% vol.) The activation time is a period of time required for alloy to reach it’s austenitic transformation (Af) temperature. For examined wire it reached values up to 60 °C. Heating of NiTi wire was conducted by retaining heat. In this paper the influence of wire length and electric current power on heating time is presented. This research allows to determine the correlation between the increase of temperature and time. For given electric current values. This data  is useful for effective design of SMA actuators.