"I will answer only my lawyer," said Cristina, King Felipe VI's sister, who denies being an accessory to tax evasion.
In answering only the questions of her own lawyer, the royal refused to answer questions posed by the prosecution or the other defence lawyers.
Cristina also denied knowledge of her husband Inaki Urdangarin's activities and expressed her full confidence of his innocence:
"I completley trust my husband and am convinced of his innocence," she said.
Cristina explained how her husband had "managed the financial side" of the family and she "managed our schedule".
Princess Cristina was questioned for just over 24 minutes on Thursday.
Distancing herself from her husband Inaki Urdangarin's business affairs, she told the court she trusted him and never asked about the dealings of a company they co-owned which operated from an office in their Barcelona mansion.
The couple went on trial along with 15 others in January in a case that has sullied the reputation of the monarchy and become a symbol of perceived corruption among Spain's elites.
The case centres on accusations that Urdangarin, a former Olympic handball medallist, used his royal connections to win inflated public contracts to stage sporting and other events and then syphoned off the proceeds to fund a lavish lifestyle.
He and his former business partner Diego Torres are accused of embezzling about six million euros ($6.6 million) in public money that was paid to the Noos Institute to organise events.
One of the companies that allegedly benefited from Noos was Aizoon, a real estate firm that Urdangarin owned with Cristina, the youngest daughter of former King Juan Carlos I who abdicated in June 2014. Aizoon has been labelled a "front company" in court documents.
The princess is accused of making personal use of Aizoon funds to pay for items such as clothes and dance lessons for the couple's children, as well as work on the couple's Barcelona mansion, lowering the firm's taxable income.
Cristina, a 50-year-old mother-of-four with a master's degree from New York University, was a member of the board of Aizoon but said she never attended company meetings.
"I did not know Aizoon's expenses," he said.
Asked why she agreed to set up Aizoon with Urdangarin, she said: "My husband asked me and I accepted."
If convicted Cristina faces a jail term of up to eight years. Urdangarin, who has been charged with the more serious crimes of embezzlement, influence peddling, forgery and money laundering, faces more than 19 years in prison.
Sixth in line to throne
The court case follows allegations levelled by the anti-corruption group "Manos Limpias" or "Clean Hands".
The trial is being held in a makeshift court set up in a public administration school on the outskirts of Palma on the Mediterranean island of Majorca to accommodate the huge numbers of journalists covering the trial. It is expected to wrap up in June.
Earlier on Thursday Urdangarin testified that his wife was not involved in running Aizoon.
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The first defendant to take the stand, Jose Luis Ballester, a former Olympic sailing gold medallist and friend of Urdangarin, told the court last month that the head of the government of the Balearic Islands at the time, Jaume Matas, awarded contracts without competing bids to the Noos Institute.
Ballester was director general of sport for the government of the Balearic islands at the time.
The corruption scandal, as well as health woes, prompted Cristina's father Juan Carlos to abdicate in 2014 in favour of his son Felipe to try to revive the scandal-hit monarchy.
King Felipe VI swiftly ordered palace accounts to be subject to an external audit and promised an honest and transparent monarchy.
Last year, he also stripped Cristina and her husband of their titles of Duchess and Duke of Palma.
Cristina remains sixth in line to the throne however, a right only she can relinquish.