Abstract: A collapsible bag includes a main body, a flexible cover member, and a hand strap. The main body includes an opening, a first sidewall located at one side thereof a second sidewall located at another side oppose side to the first sidewall, and a first female adhesive member mounted to an external side of the first sidewall. The cover member has a male adhesive member mounted to one side thereof for adhesive connection with the first female adhesive member while the cover member is turned to the first sidewall to seal the opening of the main body. The hand strap is fixed to the main body. The main body further has a second female adhesive member mounted to an external side of the second sidewall thereof for connection with the male adhesive member while the main body is folded to fasten the folded main body.