Prosecutors said one of those arrested was a Syrian citizen residing in Bulgaria who is suspected of sending money to people who back what they termed international terrorist groups.
The ring is suspected of sending money abroad via the traditional Muslim hawala system which uses individual brokers rather than banks.
"The investigation is about crimes linked to terrorism financing," deputy chief prosecutor Ivan Geshev told reporters.
"The main suspect has been in contact and financed people engaged with providing logistics to international terrorist organisations and their financing," Geshev said, without naming the groups.
The police raids happened at more than 50 sites and 26 cars in seven Bulgarian towns. They seized some 32,000 euros ($36,000), documents and other evidence. They were the culmination of a year-long investigation involving other European Union countries, the prosecutor said.
He added that the investigation was not about any direct terrorist activities in Bulgaria.