Bjoern Hoecke, head of the AfD in the eastern state of Thuringia, is part of the nationalist wing of the AfD, officially designated by the domestic intelligence agency as "right-wing extremist".
The case comes at a time when the AfD, running second in national polls behind the opposition conservatives, is under scrutiny over reports that some senior party figures had discussed the deportation of people with non-ethnic German backgrounds.
About 300 protesters gathered outside the court in the eastern city of Halle on Thursday holding placards with the words "Bjoern Hoecke is a Nazi" before he entered a packed courtroom.
After some delays due to tight security, his lawyers addressed the court.
Protesters gathered outside the courtroom with placards saying "Bjoern Hoecke is a Nazi". (AP PHOTO)
Prosecutors say Hoecke ended a campaign speech in the eastern town of Merseburg in May 2021 with the words "Everything for Germany!"
This phrase is banned in Germany as it was a slogan used by Nazi SA stormtroopers.
His lawyers argue he did not know the words were banned and Hoecke himself, a history teacher, said last week in a television debate he was unaware of the origin of the phrase and says this case is about free speech.
He has also been charged with using the term at a party event in December in Gera when, prosecutors argue, he said: "Everything for ..." before using gestures to encourage his audience to say the last word for him, aware that he faced prosecution for finishing the phrase himself.
In Germany, the use of slogans and symbols linked to anti-constitutional groups, including the Nazi party, is illegal.
If convicted, Hoecke could face a fine or prison sentence of up to three years and might also be barred from public office.
Hoecke is an influential figure in the AfD, which has shifted to the right since it was founded as an anti-euro party in 2013.
He has hit the headlines repeatedly over his views, and a court has said he can be described as a fascist.
He also faces a separate trial over suspected incitement to hatred.
In the state of Thuringia, where AfD is the frontrunner in polls on about 30 per cent, the party might win most votes in a September 1 election.
But so far no other party has been prepared to co-operate with it, so it is unclear how it could form a coalition government.
