The drugs were found after Arizona resident Jorge Valdez-Rosas, 22, was arrested on Wednesday at a hotel in Upper Merion Township.
The district attorney's office says the investigation began when authorities received information that a drug trafficking organization operating in Mexico and the United States was in the process of smuggling fentanyl.
An investigation led police to Valdez-Rosas and he was placed under surveillance on Tuesday.
When he left his hotel room on Wednesday, the D.A.s' office said he was found to be carrying a duffel bag with five kilograms of fentanyl inside.
Valdez-Rosas is being held on $500,000 cash bail.