PURPOSE: To improve the quality of a thin magnetic alloy strip by forming a thin strip from the molten magnetic alloy prepared by containing one or more of small amounts of P, Al, Si and Ti, Nb, Zr in an element of Fe by a quenching process and further heat treating the alloy.

CONSTITUTION: A magnetic base alloy is prepared by containing 0.01W1.5wt% of P, 0.01W1.5wt% of total of any one or more of Ti, Nb and Zr, and 3.0W26.0wt% of total of 0.01W13.0wt% of each of Al and Si in Fe, and molten by high frequency induction heating, for example, in a quartz pipe 2 having a nozzle 1. Pressure is applied to the alloy with inert gas, and the thin strip is drawn while quenching the alloy on a rotating cooling roll 3. The thin strip is annealed at 750W1,300°C. The thin strip thus manufactured has preferable smoothness and preferable electric and mechanical properties.