PROBLEM TO BE SOLVED: To provide a folding pet carrier box.SOLUTION: The pet carrier box is composed by crossing a folding inverted U-shaped upper plate and a U-shaped bottom plate. The pet carrier box has two wing pieces for connection to be bent to the inner side on the bottom on both sides of the inverted U-shaped upper plate to connect and fix corresponding sides of the U-shaped bottom plate. The pet carrier box also has an upward front plate and rear plate on both sides of the U-shaped bottom plate corresponding to front and rear openings of the inverted U-shaped upper plate to close the front/rear openings of the inverted U-shaped upper plate. Arch-shaped folding lines are formed to be opened outward at three right, left and upper positions respectively in the front/rear openings of the inverted U-shaped upper plate, in a front gate plate and in a rear gate plate, so that respectively corresponding arch-shaped inclined angular surfaces are formed to enhance the structure strength of the box. A female implement and a male implement are disposed to be engaged and positioned with each other on the respectively corresponding arc-shaped angular surfaces, and one box body is formed by positioning the inverted U-shaped upper plate and the U-shaped bottom plate. As the inverted U-shaped upper plate and the U-shaped bottom plate can be opened and folded, the volume of the pet carrier box can be reduced, and the space can be saved.
