A packaging bag comprises a main bag body and a framework member. The main bag body is made of plastic film material through a main bag body formation process. The main bag body has an opening and a plurality of heat sealed portions. The framework member is disposed in the main bag body. The framework member is joined to the main bag body prior to completion of the main bag body formation process. The framework member is foldable/unfoldable together with the main bag body, to enable the framework member and the main bag body to be shifted between a generally flat collapsed state and an expanded state.