Police searched the homes of the eight that were arrested, as well as another 20 people suspected of supporting terrorist networks with counterfeit passports, as well as by sending supplies to Syria.
The eight men arrested were all German citizens between the ages of 22 and 35.
Federal police made one other arrest in connection with the raids, a 58-year-old Pakistani man.
Around 240 police carried out the overnight raids in Cologne and surrounding municipalities.
Police had the group under surveillance since May 2013, the Express reported Wednesday. The paper said that all those under investigation have ties to the Salafist movement.
The group allegedly broke into schools and churches, selling on stolen goods and sending the money to three jihadist networks, including Isis.