To stably manufacture a grain-oriented silicon steel sheet which has a uniform forsterite film having superior adhesion and free from defects over the overall width and overall length of a coil and also has excellent magnetic properties.

In manufacturing the grain-oriented silicon steel sheet, the ambient oxidizability (P[H2O]/P[H2]) in the course of temperature rise at decarburizing annealing is controlled, according to the amount of decrease of Si in the surface layer part of the steel sheet before final annealing and after decarburizing annealing, to a value within the range represented by y≥0.57x+0.158 (wherein, y is ambient oxidizability (P[H2O]/P[H2]); and x is the amount of decrease of Si in the surface layer part of the steel sheet).