To provide a leakage preventive structure for a roof, which can positively prevent leakage from the roof even if strong rain or heavy rain falls on an under-roofing material stapled to the roof that has not been covered with an upper roofing material such as a roof tile.

In the leakage preventive structure for the roof which is formed by stapling the under-roofing material 4 to an upper surface of a roof substrate plate 3, an agent containing an asphalt-based primer etc. having water repellency is applied to the upper surface of the roof substrate plate 3 to be stapled, and therefore water invading along the stable 5 is not absorbed in the roof substrate plate 3 but repelled by a layer 2 to which the repellency is imparted, and therefore the leakage preventive structure eliminates the problem of leakage.