Kayakujutsu (literally the art of gunpowder in Japanese) is the use of firearms, gunpowder and explosives especially by Ninja. The chapters or sections of ninjutsu devoted to the study of firearms and explosives.

The history and mythology surrounding ninjutsu and kayakujutsu are similar to the history of chemistry and the mythology surrounding alchemy. Thus kayakujutsu mysticism refers to elements like the Earth (Chi) to develop Ka (Fire) just as alchemy referred to elements just as air, earth, fire and water.