Abstract: A filter cartridge having double threads is provided, and has a housing and a cap. The housing is opaque and provided with a connecting portion, a filter containing portion and a bottom portion. The housing and the cap are tightly connected to each other by a connector. When the housing and the cap are assembled via the connector, various types of threads and shapes of the bottom portion of the housing can be selected. Additionally, users can conveniently observe the using condition of a filter media through an opened window formed on an outer circumference surface of the bottom portion of the housing and a transparent base, so that the user can then directly decide whether the filter media should be changed or not.