PURPOSE: To make crystal grains smaller without degrading the directivity of a steel plate and produce a unidirectional electrical steel plate of low watt loss by hot rolling a steel ingot contg. C, Si and a sulfide or nitride as a primary recrystallization brain suppressing agent then subjecting the same to finish annealing in a gaseous H2 atmosphere included with a slight amount of O2.

CONSTITUTION: A steel ingot or continuously cast slab contg. ≤0.08% C, 2.5W 4.0% Si and a sulfide (e.g. MnS) or nitride (e.g. AlN) as a primary recrystallization suppressing agent is hot rolled. Next, the steel ingot or the like after the hot rolling is subjected to a hot rolled plate annealing and quenching process consisting of annealing at below 1,200°C and a quenching process below 1,050°C then to a cold rolling process of 70W90% drafts whereby it is made into product plate thickness, after which the plate is subjected to decarburization annealing by a known method. Next, an annealing separating agent is coated on this decarburization annealed plate, after which it is subjected to finish annealing in a gaseous H2 atmosphere included with 30W1,000ppm O2, whereby the intended unidirectional electrical steel plate is produced.