In this work we report that amorphous alloy (Fe6Co88Ni3V3)75Si10B15 is suitable for transformer at high frequency, transformers. It has been found that optimum performance at high frequency can be achieved by high temperature annealing. The core loss at 20 kHz and 5 kG is about 18–20 W/kg. Optimum core loss is equal to 15 W/kg, which is the lowest value ever reported. This kind of amorphous alloy has good thermal and mechanical stability.