According to press reports, the gang worked through a network of around 250 shops, and the postal service has so far filed complaints against 70.
A police raid outside Stockholm reportedly uncovered at least 700,000 fake stamps, worth around half a million dollars. The postal service says 30 different designs have been faked.
The police reportedly believe the counterfeits were made somewhere in Asia.
The quality of the fakes is said to vary. Some have spelling errors, while others are reported to be high quality copies, and the only way to discern them from real Swedish stamps is with ultraviolet light.
Four people were charged in connection with the case Wednesday morning.