Disclosed is a pet bag formed to be changeable into a mat for a pet so as to improve convenience and minimize items to be carried when going out with the pet. The pet bag comprises: an inner sheet member capable of being folded, into three parts along a longitudinal direction, from a state in which the bag is unfolded in a mat state, and formed such that one end portion and the other end portion of each of the three folded parts overlap each other and are coupled to each other so as to be changed into a bag state; an outer sheet member capable of being folded, into three parts along the longitudinal direction, from a state in which the bag is unfolded in the mat state, formed such that one end portion and the other end portion of each of the three folded parts overlap each other and are coupled to each other so as to be changed into the bag state, and provided to the inner sheet member so as to be detachable therefrom; and a strap member provided to the outer sheet member so as to be detachable therefrom.
