Ethiopian, Somalian and some of other african nations also claim to be Eritreans to get an better asylum seeker status.
German customs officers have seized packages containing Syrian passports and police suspect they are being sold illegally to asylum seekers.
A finance ministry official said both genuine and forged passports were in the packets intercepted in the post.
Germany is letting Syrians register for asylum regardless of where they entered the EU. As refugees from the Syrian civil war, most have a right to asylum.
The passports can help fraudulent claimants to get asylum, the EU says.
The ministry official declined to say how many Syrian passports had been found in the customs checks. The German police are now investigating.
The EU border agency Frontex says trafficking in fake Syrian passports has increased, notably in Turkey.
A Frontex official, Fabrice Leggeri, told French radio station Europe 1 that “people who use these fake passports mostly speak Arabic.
“They may come from North Africa, the Middle East, but they have the profile of economic migrants,” he said.
Germany has by far the highest number of asylum applicants in the EU, many of them Syrians and Afghans, but many also from the western Balkan countries.
Turkey is a major transit country for refugees and other migrants heading for the EU, and is also housing more than two million Syrian refugees in camps.