A method for producing diet food using opuntia ficus indica fruit, includes: a sour dough kneading step for producing a first sour dough by using ingredients including opuntia ficus indica fruit powder a second sour dough kneading step for producing a second sour dough by mixing the same amount of ingredients as in the first sour dough kneading step with the first sour dough a main dough kneading step for producing a main dough by adding water, cereals, saccharides, nuts and other ingredients to the second sour dough a first fermentation step for fermenting the main dough by introducing the same into a fermentor and a food producing step for producing food by using the main dough fermented by the fermentation step, wherein the second sour dough kneading step is performed under a relatively lower temperature condition than the first sour dough kneading step.
