The detainees refused to sign the pledge, said the Umma Islamic Party, which was formed earlier this month by 10 university professors, political activists and business people,
Political activity in oil-rich Saudi Arabia, which follows strict Islamic rule, is severely restricted and all power rests in the hands of the ruling family. The fledgling signs of political demands in Saudi Arabia come at a time when pro-democracy protests against authoritarian governments are sweeping the Arab world.
The Umma Islamic Party has urged the kingdom's rulers to start a dialogue on reform, including improving the status of women.
In a statement e-mailed to The Associated Press, the party said all founding members were arrested Wednesday.
One of the founders, Sheik Mohammed bin Ghanim al-Qahtani, was quoted as saying he and the others did not commit a crime to justify the arrest and that they were exercising legitimate political rights.
The arrests will only "increase the political tension among the Saudi people who, like other Arab peoples, aspire to real political reform based on their right to freely express their opinions, hold political gatherings and elect their lawmakers," the statement said.
The party called on the government to release its founding members.