This invention relates to an inhibitor of lead-induced stress corrosion cracking including nickel boride in the secondary side of steam generator tubes in nuclear power plants and an inhibition method using the same, and more particularly, to an inhibitor of lead-induced stress corrosion cracking, in which nickel boride is added to secondary side cooling water of the steam generator in an amount of 0.2˜6 g/l, and to an inhibition method using the same. According to this invention, when the inhibitor of lead-induced stress corrosion cracking is added to the secondary side of the steam generator tube in nuclear power plants, stress corrosion cracking of the tubes, which occurs in the lead-containing neutral or caustic solution, and a crack growth rate are decreased, thus increasing elongation. Further, a stress corrosion cracking ratio is decreased, and therefore the stress corrosion cracking resistance of metal or alloy can be improved. Therefore, nickel boride can be usefully used as an inhibitor of lead-induced stress corrosion cracking of the steam generator tubes in nuclear power plants.