A developer supply container includes a cover plate mounted on an outer surface of a container body and provided with an opening corresponding to a developer supply port of the container body, which is sealed by a seal tape. The seal tape has a folded section extending through a gap between the container body and the cover plate and a through hole of the cover plate such that an end portion of the seal tape is exposed. A seal piece is mounted on an outer surface of the cover plate. On the outer surface of the container body a door member is slidably mounted. The developer supply container can prevent developer from leak out and has a good manufacturing yield rate.