An oriented silicon steel sheet with a very low core loss and a process for producing it at a lower cost are disclosed. The steel sheet consists essentially of Si: 1.5-3.0%, Mn: 1.0-3.0%, sol. Al: 0.003-0.015%, with Si (%)-0.5.times.Mn (%).ltoreq.2.0 and the balance being Fe and incidental impurities, in which the amount of C and N as impurities is not more than 0.0020%, with S being not more than 0.01%. This steel sheet can be produced from a slab containing up to 0.01% C and 0.001-0.010% N through hot rolling, cold rolling, primary and secondary recrystallization, and then decarburization.