Fe－6.5%Si (mass fraction) alloy exhibits excellent soft magnetic properties and therefore is very suitable to be used as iron core in high frequency electromotor. However, the room－temperature embrittlement and poor workability limit the practical applications of the alloy and it is hard to be fabricated to thin sheet. It is reported that ultra－thin sheet with 0.05 mm in thickness has been successfully obtained by an advanced technique of stepwise ductilization, including hot, warm and cold rolling processes with intermediate heat treatment. And suitable heat treatment can improve the ductility of this alloy sheet, therefore it plays an important role in this technique. However, the existing heat treatment is time consuming and not suitable for industry. In this work, effects of heat treatment on mechanical properties of the hot－rolled sheet have been investigated in dependence of annealingtemperature and time. The experimental results show that heat treated Fe－6.5%Si sheets have better mechanical properties than those of as hot－rolled sheets. Elongation of heat treated sample is twice as hot－rolled sample's and hardness decreases significantly. Also it is found that heat treatment at  850℃ for 1 min and then quenching in brine provides good ductility and low hardness, which is benefit to the subsequent processes and increases the productivity substantially.