The current and former president of the club denied wrongdoing at the court in Madrid on Monday.
Barcelona said it paid Brazilian club Santos €57m (£43m) for Neymar, 23, with his parents receiving €45m of the fee.
But investigators allege the fee was closer to €83m and that Barcelona should have paid another €13m in tax.
Barcelona Football Club president Josep Maria Bartomeu and his predecessor, Sandro Rosell, all deny defrauding the tax office.
In a statement on Monday, the club said they had repeated what they had told the court last year, namely that Barcelona had acted correctly. "They are not worried and said they have confidence in justice," it added.
Neymar`s father and mother were also set to appear at the National Court in Madrid on Tuesday.
The case was brought by Brazilian third-party investment fund DIS, which owned 40% of the Brazilian player`s sports rights. DIS alleges it was financially harmed by the transfer as part of the fee was concealed.
Judge Jose de la Mata was expected to decide whether Neymar`s parents were to give evidence in person.
Neymar`s move to Barcelona has been a big success on the pitch. The striker became part of a goalscoring trio with Lionel Messi and Luis Suarez.
In 2015, he helped the club win five trophies and came third in the Fifa Ballon d`Or competition. He also scored in the Uefa Champions League final against Juventus.
But he has also encountered legal difficulties in Brazil, where a court has frozen $47m (£33m) of his assets in connection with suspected tax evasion between 2011 and 2013.
Neymar to appear in Barcelona tax fraud trial
02 February 2016
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Brazilian footballer Neymar is due to give evidence in a Spanish court over allegations of tax fraud surrounding his transfer to Barcelona in 2013.
